Coastal SEES: Sea-level change and thresholds for coastal water sustainability

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I. INTRODUCTIONThis proposal addresses a central question: To what extent are water resources (both

fresh and salt) in coastal zones sustainable in the face of accelerating sea-level rise and population growth? This question stems from uncertainties of how sea-level change impacts coastal water resources at various time and spatial scales. Uncertainties arise from multiple linked physicochemical, biological, and human processes occurring at coastal zones (Fig. 1)1 that require interdisciplinary research for adequate responses and adaptations. Responses and adaptations to sea-level rise must occur at optimal times, otherwise they may become prohibitively expensive or impossible to accomplish once changing conditions pass certain thresholds (abrupt changes in rates or conditions)2,3. Therefore, this project aims to provide process-based understanding of sea-level effects on coastal water resources as a pathway to improving their sustainability by addressing four ancillary and related questions linked to our over-arching question, specifically: What are potential rates of sea-level change and how will they impact water resources for

human and ecological services? What natural processes and human behaviors have thresholds that when passed will degrade

water resources? How will crossing thresholds impact natural and built coastal environments? How do thresholds vary with hydrologic characteristics of coastal aquifers?

These questions lead us to develop four specific hypotheses (Section III) to be tested using a work plan (Section IV) of collaborative interdisciplinary field observations, experiments, laboratory analyses, and modeling. Broader impacts (Section V) include development of an interdisciplinary STEM workforce, contributions to site-specific coastal management, and public outreach. Our questions, hypotheses, and work plan arise from results of a Track 1 Coastal SEES planning project (Section II) that allowed us to assemble this multidisciplinary team of PIs and provided us with excellent working relationships and communication abilities.

II. RESULTS FROM PRIOR NSF SUPPORTA. Martin, Ogram, Peng, Valle-Levinson, OCE-1325227, $441,125, 8/15/2013-

7/31/2015 (plus 1-yr no-cost extension), “Coastal SEES (Track 1): Planning for hydrologic and ecological impacts of sea-level rise on sustainability of coastal water resources”.

Intellectual Merit: This project (hereafter referred to as CS1 for “Coastal SEES Track 1”) accomplished interdisciplinary field observations, laboratory analyses, and modeling that were used to assess how sea-level change affects human communities, water resources, coastal hydrodynamics, microbial community structures and functions, and biogeochemical reactions at various time scales (Fig. 2). The project focused on two coastal settings representing end-member subterranean estuaries (STE)4: the east coast of Florida, USA and the east coast of Quintana Roo, Mexico (Yucatan peninsula). Both sites discharge fresh water to coastal lagoons: the Florida STE from

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Fig 1. Linkages between disciplines required to understand sea-level rise effects on coastal water resources.

a granular siliciclastic aquifer and the Quitana Roo STE from a carbonate karst aquifer (Fig. 3). These two regions have experienced recent rapid population growth. They constitute the field sites for this proposed project.

Our CS1 results show that hydrogeology and biogeochemical reactions at both sites depend on aquifer characteristics and short-term (tidal to decadal) sea-level variations. In Quintana Roo’s karst STE, fresh and brackish water discharge via conduits (water-filled caves), but reverse flow (backflow) occurs when sea level rises above a threshold of 0.08 m above the average sea-level elevation during our fortnightly observation periods

(Fig. 4)1. During backflow at elevated sea levels, oxygen-rich lagoon water flows to the aquifer and catalyzes biogeochemical reactions. During discharge, reaction products, including nutrient-rich water, flow to the lagoon (Fig. 3). Switching from discharge to backflow was modulated by spring-neap tidal cycles and wind set up 1,5,6. Biogeochemical reactions reflect changes in microbial community structures7,8 although understanding community functions requires additional samples9. We predict backflow-discharge timing and magnitude will change as water demand, which has risen from 29 to 873 x 106 m3 between 1980 and 2012, increases with population growth10.

In the granular aquifer (Florida), the location of the seepage face (the coastal zone discharging fresh water11) has shifted shoreward by tens of meters as the lagoon flooded following the Last Glacial Maximum12. Data from CS1 extend previous observations to nearly 10 years and show ~5 m (~25%) shoreward migration of the seepage face (Fig. 5). We speculate based on tide gauge data that the shoreward shift in seepage face width reflects acceleration of sea-level rise throughout the South Atlantic Bight by about 10-fold to rates of ~20 mm/yr over the past 5 years13. In addition, data from CS1 indicate freshwater seepage faces range in width from zero to nearly 50 m offshore throughout Indian River lagoon, reflecting heterogeneity of recharge and hydraulic properties of the aquifer.

Biogeochemical reactions are similar at both study sites and include enhanced organic matter remineralization, carbon cycling14, altered N speciation15, sources of P from organic matter and carbonate minerals1, reduced metal oxides, sulfate reduction and sulfide oxidation12,16,17, with resulting pH changes, mineral dissolution and changing sources and sinks of P1. These similarities are reflected in microbial community structures9,18 and occur regardless of differences in time and spatial scale of STE responses to sea-level change (e.g., Fig. 3). This observation indicates general results may be obtained for how sea-level impacts coastal water resources from these end-member sites. Publications: To date, 6 abstracts and meeting presentations9,14,15,19-21, and 4 papers have been published or submitted for publication1,5,6,13 and at least 3 more papers are in preparation for the peer-reviewed literature10,18,22

Broader Impacts: CS1 integrated interdisciplinary activity at the University of Florida (UF) centered on coastal water resources and sea-level rise. Coupling CS1 with a UF Water

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Times scales of the various processes that impact sustainability of coastal water resources on which we will work.

Institute Graduate Fellows (WIGF) Program supported the research of 10 PhD-level graduate students, one post-doctoral researcher, and two additional faculty members. Participants represent five departments (Geological Sciences, Coastal Engineering, Soil and Water Science, Urban and Regional Planning, Wildlife Ecology) and four colleges (Liberal Arts and Sciences;

Engineering; Agriculture and Life Sciences; Design, Construction and Planning), reflecting the range of disciplines involved. One of the additional faculty members (Dutton) helped develop this proposal with her prior NSF support (Section IIB) and is a co-PI on this proposed project.

Our work in Quintana Roo established synergistic activities with Mexican colleagues at CINVESTAV-IPN and Centro de Investigacion Cientifica de Yucatan, in Merida, and at Universidad Nacional Autonoma de Mexico and Parque Nacional Arrecife in Puerto Morelos, including collaborative work with two faculty there and four of their graduate students (2 PhD and 2 MS)1,19. Our work in Indian River Lagoon provides estimates of benthic nutrient fluxes from the STE in support of the St. Johns River Water Management District (one of five Florida water management districts) efforts to prepare a nutrient reduction model to manage harmful algal blooms.

B. Dutton Sole-PI; OCE-1155495, $314,258; 4/1/12 – 5/31/16, “Towards a Global Reconciliation of Last Interglacial Sea-Level Observations”

Intellectual Merit: Given the current inability to project dynamic instability of ice sheets under future warming scenarios, the behavior and dynamics of polar ice sheets during past warm periods provide indispensable empirical constraints. This project aims to reconcile observations of the magnitude of peak sea level during the last interglacial period and sea-level minima associated with glacials MIS 2 and 6 through fieldwork to survey and collect samples, U-Th dating of corals, and glacial isostatic modeling. Publications: Three papers have appeared in the peer-reviewed literature 23-25 another two student-led manuscripts are in preparation26,27; at least three more are anticipated; 14 abstracts (6 posters/8 talks, references) presented by the PI and a PhD graduate student at domestic and international conferences.

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Fig 3. Spatial scales, flow paths and distribution of biogeochemical reactions at two end-member STEs: Quintana Roo: a) karst STE during backflow at elevated sea level, b) karst STE during discharge at low sea level, and Florida: c) granular STE with less dynamic flow conditions than karst systems.

Broader Impacts: The grant has supported three graduate students, one undergraduate researcher, a class of students who participated in collection of field data in the Bahamas, a video exhibit and a new exhibit on sea-level change being developed in collaboration with the Florida Museum of Natural History. Publications in QSR and Science received significant media attention. The Science paper was picked up by more than 25 media outlets globally including Reuters, The Guardian, and The Washington Post. Research from this grant has been featured twice by NSF (on their home page in Jan-2015 and as the top news story for Science360 in July-2015). This media attention directly led to further engagement in public outreach to communicate the research results, including involvement in an upcoming feature film about climate change and a documentary series on

climate change being produced by National Geographic (with an episode focused on sea-level rise in south Florida), contributing to an in-depth piece for the New York Times Magazine, and being consulted in-person by U.S. Senator Bill Nelson (D-FL) regarding sea-level rise in Florida.

III. HYPOTHESES AND SIGNIFICANCE

A. Hypotheses to be testedHypotheses proposed here center on the overarching hypothesis that sustainability of

coastal water resources depends on rates of sea-level change, consumption and degradation of water resources, biogeochemical transformation at the fresh-salt water interface, and physical connections between fresh and salt water. We break this general hypothesis into four specific hypotheses to be tested by our interdisciplinary work plan of linked and simultaneous observations, experiments, models, and analyses (Section IV). Our work plan describes specific objectives designed to test the following hypotheses individually and through synthesis of each objective’s outcomes. Specific hypotheses and tests are:

Hypothesis 1: Sea-level rise and coastal population growth will degrade coastal water resources at dissimilar spatial and temporal scales. This hypothesis will be tested through comparing extant observations and projections of coastal development and population growth with evaluations of potential rates of sea-level change based on sediment archives during the last interglacial period ~125,000 years ago (centennial to millennial rates), observations from tide gauge data (decadal rates), and direct observations (seasonal, storm and tidal scales).

Hypothesis 2: Water resources will degrade abruptly when thresholds in population densities, sea level, water table elevations are crossed. This hypothesis will be tested through high-resolution observations of changes in sea level and inland water table at intra-tidal to

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Fig 4. Two-week time series at Pargos spring, Quitana Roo. Top: Deviation from mean water level and distribution of genes. Middle: Salinity of lagoon and within cave. Bottom: Dissolved oxygen and pH within cave.

seasonal time scales; analyses of the impact of changing levels on salt and water exchanges between coastal and aquifer water in two end-member types of STEs; measurements of exchange effects on solute (e.g., C, N and P) concentrations; and compiling, modeling, and comparing data related to inland fresh water consumption relative to changes in water table elevations and population growth.

Hypothesis 3: Exceeding thresholds will alter microbial community structures and functions, nutrient delivery, and salt fluxes; degrade potable water resources; increase cost of human adaptation; and reduce efficacy of adaption measures. This hypothesis will be tested by compiling water resource usage data and measuring water table and sea-level variations at seasonal and shorter time scales. These data will be compared with simultaneously measured changes in microbial communities and functions, chemical compositions of water, shifts in hydrodynamic behaviors, and possible contamination from the built environment. These comparisons will be made in the framework of past rates of sea-level change based on sediment archives and projections of future sea level and water usage.

Hypothesis 4: Crossing thresholds depends on hydrologic characteristics, especially permeability, of the coastal aquifers comprising the STEs. This hypothesis will be tested by comparing data from two end-member STEs, both in rapidly developing settings. One STE is composed of granular siliciclastic sediments with diffuse flow, and the other STE is composed of

variably lithified carbonate rocks and sediments with conduit flow (Fig. 3).

B. Scientific SignificanceEustatic sea level is rising at

~3.2 mm/yr and projections suggest that if the rate accelerates as expected, sea level will be 0.26 to 1.90 m higher than present by 210028-

30. Rising sea level represents a slow-moving problem, punctuated by short-term disasters (e.g., Hurricanes Katrina and Sandy) for the more than 1 billion people who live along coasts31. Particularly vulnerable areas include densely populated regions of Southeast Asia, Egypt, and sub-Saharan countries32 and the US where ~123 million people (39% of the population) live in coastal counties33. Although attention-grabbing events such as storms, storm surge, flooding, and increased erosion are clear

threats34, less attention is focused on threats to coastal water resources (both fresh and salt) from rising sea level and increased population, which may limit coastal-community sustainability prior to inundation. Threats to freshwater resources include over pumping, waste disposal, and related effects of increasing coastal populations35,36. Threats to salt water resources, which support coastal ecosystems and economies, include changed solute fluxes from reduced submarine

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Figure 5. Two of 10 profiles measured over the past decade at one seepage face of the Indian River Lagoon STE, showing scale of landward movement of the salt /fresh water interface. Colors represent salinity. White dots represent sampling ports of multi-level piezometers.

groundwater discharge37,38 and altered compositions following reactions caused by salt water intrusion1.

Rates of sea-level rise vary through time as shown by sea-level reconstructions that span timescales of 10-105 years e.g.39,40 and direct observations based on tide gauges and satellite altimetry28. Sea level rose 3 meters on ecological time scales based on spectacular successions of reef facies at Xcaret in Quintana Roo from the last interglacial41,42. A similar rapid rise is shown by reef exposure surfaces in the Bahamas and Florida, but these sites suggest an ephemeral sea-level fall of at least 1 meter preceded the rise. These rapid changes in sea level reflect the instability of polar ice sheets during warm climates43,44. Instabilities also appear from meltwater pulses45 as sea-level rises of 1 to several meters over 102 to 103 years occurred during retreat of Northern Hemisphere ice sheets over the past 20,000 years. The potential for future rapid sea-level rise rates is shown by the recent finding that the West Antarctic ice sheet is susceptible to collapse46. Understanding potential rates of sea-level change is thus critical to develop adaptation strategies for coastal ecosystems and human communities.

Recent accelerations of sea-level rise are shown by tide gauge and satellite altimetry data, which reveal a change from a global mean rate of ~1.2-1.9 mm/yr between 1901 and 1990 to ~2.8-3.7 mm/yr from 1993-201047. Rates also vary spatially; tide gauge data show ~5 mm/yr rise along the Mid-Atlantic Bight over the past couple of decades48-51. These rates, which are in excess of the global average, reflect wind forcing, deceleration of the Gulf Stream, and changes and/or divergence in the Atlantic Meridional Overturning Circulation52-54. Rapid sea-level rise also began recently in the South Atlantic Bight, with tide gauges showing rates of ~18 mm/yr since 2011 13,55. These rates may reflect changes to the Atlantic Multi-decadal Oscillation and slowing of the Florida current56,57. Temporal and spatial variations in sea-level rise should alter biogeochemical processes in STEs and impact sustainability of coastal water resources, depending on hydrodynamic connections between coastal and aquifer waters (Fig. 3). Rates of sea-level change and absolute elevations thus represent important thresholds that, when exceeded, could permanently degrade coastal water quality.

Human behavior and development are going to be impacted by these variably rates of sea-level change. Human behavior can also alter natural coastal processes. Consequently, understanding rates of sea-level change and natural coastal processes is required to develop predictive models, translate these models to policy, and develop adaptation strategies35. As coastal populations grow and coastal lands are increasingly developed, water consumption is expected to increase as water supplies drop when rising sea level shrinks water availability. Rising sea level and population growth also complicate the ability to treat storm and waste water. Balancing water demand and supply is thus critical and will require understanding how potential thresholds of sea level may affect coastal human communities as thresholds in water demand and supply balance are reached. Results of natural process studies when linked to human-induced thresholds of water demand will also have to be interpreted based on past, current, and projected rates of sea level change, on whether the rates are accelerating or decelerating, and on how rates control hydrodynamic and biogeochemical processes in the coastal systems.

Sea level change will first affect hydrodynamic and biogeochemical processes in STEs4, locations critical to sustainability of coastal water resources. They receive the first effects of salt water intrusion as sea level rises36,58 and impacts will be modified by changing elevations of the groundwater table59-61. Subterranean estuaries provide a source of ecologically important solutes including nutrients62-65 and metals66-68 to coastal zones. Nutrient fluxes may decrease with salt water intrusion or may increase as inland vadose zones shrink, limiting waste disposal options.

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Salt water intrusion should alter microbial community distributions and functions in STEs, thereby altering biogeochemical reaction and nutrient fluxes65,69-71. Microbial community functions should be affected as dissolved oxygen (DO) and dissolved organic carbon (DOC) concentrations, compositions, origins, and lability change14,69,70,72-74. Organic carbon remineralization will alter compositions of the greenhouse gases carbon dioxide (CO2) and methane (CH4), nutrients including N and P, and toxins such as sulfide75. These changes will negatively impact coastal economies, for example from diminished fisheries and tourism, as estuarine water quality degrades. Each of these processes may change abruptly, and possibly permanently, as sea level and water use surpass still unknown thresholds.

The multiple natural and anthropogenic processes that impact coastal water resources (Fig. 1) require collaborations between natural and social sciences to develop adaptation strategies35. Combining natural and social science observations, proxy information, legacy data, and models will be challenging, but is necessary to understand rates of sea-level change, its control on coastal hydrodynamics and hydrogeology, its control on exchange and mixing and associated effects on biogeochemical reactions, how it may degrade water quality and quantity for human and ecological use, and how human behaviors impact and respond to these processes. Developing this understanding should provide pathways toward sustaining coastal water resources, the primary goal of this proposal. To reach this goal, our project integrates hydrology, coastal hydrodynamics, biogeochemistry, microbiology, and geology with social sciences including economics and regional planning as a means to develop an understanding of the relationships between changing sea level, human activities, and coastal water resources.

IV. WORK PLANCritical variables in sustainability of coastal water resources include relative elevation

(i.e., hydraulic heads) and rates of change of sea level and inland water table, which control hydraulic gradients. Changes in elevations affect hydrodynamics and hydrogeology of coastal zones and thus water compositions, microbial communities and functions, and sustainability of water resources for coastal human communities. Our work plan examines these variables at the two contrasting sites established with CS1 (Section II): the east coasts of Florida and Quintana Roo (Fig. 3). We will test our hypotheses through interdisciplinary field observations, laboratory analyses and experiments, and modeling by addressing objectives linked to each hypothesis. We acknowledge that detailed descriptions of work plans typically provided for single disciplinary proposals is restricted here by the involvement of multiple PIs and disciplines combined with a limited proposal length. Our description thus condenses each disciplinary approach, methods, and expected outcomes to highlight the synergies achieved by merging these disciplines to address our science questionsthe objectives.

A. Objective 1: Assess variable rates of sea-level rise and human water needsExtant tide gauge observations are too short to determine rates of sea-level change

associated with warmer temperatures and continental ice sheet collapse, forcing us to rely on sea-level archives in the geological record. Here we focus on fossil coral reefs in Florida and Quintana Roo, and speleothems from Quintana Roo from the last interglacial period, when sea level peaked some 6 to 9 m above present76-78. These rates of sea-level rise will be used to evaluate their potential to impact human water needs within built environments in coastal communities. Tasks within objective 1 thus include sampling geologic deposits to estimate

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possible variations in sea-level change and applying these rates to assessments of the vulnerability of coastal water resources.

(1) Estimates of changing sea-level rates. To reconstruct the nature and rates of sea-level change, we will survey elevations of fossil corals that grew during a past warm period, undertake detailed paleo-depth analysis of assemblages of reef biota and diagenetic fabrics, and combine these observations with radiometric U-series ages to determine timing and rate of sea-level change. Both field sites provide evidence of rapid sea-level rise and an influx of sedimentation in the coastal lagoon ~117,000 yr ago; however, these events are not well-dated so the timing is only loosely constrained. Although not a part of CS1, initial reconnaissance work (fossil reef and speleothems) has been accomplished and local connections have been established in both field sites that allow us to develop the three tasks described below.

Task 1 (Fossil reef at XCaret): We will revisit the Xcaret site on the Yucatan Peninsula, which preserves two distinct reef terraces. We will collect samples from the lower reef tract, across the transition zone between the two reefs, and into the upper reef by drilling into the reef. This work will be done in collaboration with local expert Dr. Paul Blanchon at UNAM (see letter of collaboration). We will use carbonate petrographic techniques to identify cement stratigraphies and exposure history that record shifts from marine to fresh water and back to marine, reflecting sea-level oscillations. Previously collected detailed coral assemblage data41 will be used to complement the interpretation of sea level and reef response. For example, a distinct layer of sediment-tolerant corals and coralline algae represents reef demise in the transition from lower reef and the upper reef. Our approach of correlating stratigraphies, ages, and taphonomies of the corals will help determine if reef demise was due to a rapid sea-level fall or rise and improve understanding of the reef and coastline response to rapid changes in sea level.

Task 2 (Rio Secreto Caves near Xcaret): Due to high uncertainty in ages of the corals previously dated from Xcaret42, we will complement the reef record with age data from stalagmites at nearby caves that have a greater potential to provide robust age constraints for local sea-level changes due to their resistance to chemical alteration79. Stalagmites form only when caves are above sea level, and thereby provide constraints on timing and magnitude of sea-level changes79-81. Therefore, by dating the age of the stalagmites with U-series radiometric dating techniques, we can identify when they stop and start growing, and document the timing of cave submergence and the rate of sea-level rise across elevations in the cave. We will collect stalagmites in portions of the Rio Secreto caves normally not open to the public (see letter of collaboration). These caves occur at optimal elevations to capture the transition into and out of the last interglacial highstand. Recent work at a nearby cave produced an age of ~117,000 years for inception of stalagmite growth, when sea level fell at the end of this warm period82. Stalagmites will be collected, first as small samples from their top and base (without removing the whole specimen) to guide our strategy for sampling of whole stalagmites, which will provide the highest resolution sea level-age relationships. This sampling approach minimizes impact to cave deposits, which are in an ecological preserve.

Task 3 (Fossil reef in Florida Keys): Reef deposits in the Florida Keys will be studied to evaluate potential sea-level variations in eastern Florida and between study sites (refs). Here we will use the same U-series dating methodology as at the fossil reef site at Xcaret (Task 1). Four drill cores into the reef will come from two locations: Windley Key and Lignumvitae Key, where fossil reef material preserved at the outcrops represents the highest elevations in the Keys. Both the Windley Key quarry and Lignumvitae Key are Florida State Parks and we have permits to

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conduct sampling required for this project. We will use a portable rotary drill with a diamond drill bit and wireline system that is capable of 30 m penetration and excellent core recovery. The drill has been successfully used in many previous coral reef drilling projects83-85 and can be transported by boat, which is the only access to Lignumvitae Key.

New data generated from these tasks will inform other portions of this project of potential rates of sea-level change at our study sites. These rates should allow us to predict values of sea level threshold elevations and when they may be exceeded by coupling the rates with estimates of how water and microbial compositions and the built environment respond to short-term observations of sea-level change as described in the following sections.

(2) Water stress in the built environment. How Impact of variations in rates of sea-level rise may impacton coastal human communities will be evaluated using an integrated water demand-supply model to assess water stress in differing sea-level rise scenarios. Relationships between water demand and available water resources reflect a threshold that may be crossed when demand exceeds supply, which will depend on rates of sea-level rise. To assess the potential for crossing this threshold, we will conduct vulnerability analyses of fresh water resources in the coastal human communities based on our estimates of sea-level rise rates and a water balance model.

The water balance will be based on potential recharge and demand, and used to assess water stress in the coastal human communities of our study sites. This balance is determined by precipitation, water usage, transpiration and evaporation, seawater intrusion and other factors. Each community may exhibit different water-stress levels because of their location, population, land cover and local potential rates of sea-level rise, e.g.13,42,55. The water balance may be written as

R v=∑i

❑

( Pi−U i−T i )+ I +O

where Rv is total groundwater recharge, i is geographic location, P is average seasonal precipitation, U is total groundwater use, T is evapotranspiration, I is groundwater change by seawater intrusion, and O is other influencing factors such as surface runoff, interceptions, and leakage assumed to be unchanged at short time scales. Groundwater usage (Ui) is the sum of domestic, industrial, commercial and agricultural usage, which is determined by population, meteorological conditions, land use, and per-capita use. These variables will be calculated in geographic units using Geographic Information Systems (GIS) for both study areas. We expect water resources to respond differently to potential sea-level rise in these two regions as a result of dissimilarities in infrastructure, water demand, recharge, aquifer characteristics, population growth rate, and different rates of sea-level change.

We will also perform a vulnerability analysis that will include variations in estimated future sea-level rise rates, movement of the saltwater/fresh water interface, water quality from the water chemistry and microbe analyses (section IV.C), and water demand for consumption by human activities. Additional risks arise from flooding vulnerability, which we will estimate based on our sea-level rise estimates, elevation of the area, land-use types, and property values using GIS. The results of the water vulnerability analysis will predict risk levels of fresh water shortage and degradation of water quality within the two study areas. Results of the vulnerability analysis will be used to estimate the economic costs of sea-level rise and study human responses in the coastal communities. The economic costs, including direct and indirect costs, of sea-level rise will be estimated based on the Computable General Equilibrium model86,87, in which the multiplier costs to the inter-dependent industrials will be determined.

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B. Objective 2: Evaluate potential thresholds of sea-level change and water qualityExpected alterations of coastal water systems from sea-level rise will be evaluated

through observations of fluctuations in sea level at various time scales caused by processes such as tides1,5,6, storm set up1,6,88, and ocean-current forcing89. Task within objective 2 thus include sampling and observing sea-level variations and water compositions at our two sites over short-term time scales (< 1 sec to decadal, Figs. 3, 4, and 5) to assess physicochemical responses to the sea-level changes, as well as paleo-reconstructions of lagoon water compositions based on coral geochemistry.

(1) Hydrodynamics. In the slowly responding granular STE of the Indian River Lagoon, we will make new hydrodynamic observations at our three currently instrumented seepage faces (e.g., Fig. 5) and couple them with hydrographic data to be compiled from infrastructure operated by NOAA and NDBC (tidesandcurrents.noaa.gov; www.ndbc.noaa.gov/hmd.shtml), including lagoon and off-shore water levels. These records will be supplemented by installation of Conductivity, Temperature, Depth (CTD) sensors in wells onshore and at two depths in piezometers across the seepage face. The piezometers will be surveyed to a common benchmark. Temporal variations in water elevations will be compared with changes in conductivity and temperature to observe how seepage faces respond to changing lagoon elevations through storm e.g.90 and longer events. These results should inform us which water levels could represent thresholds that change flow conditions and water chemistry.

We will expand fortnightly observations made over the past two years (Fig. 4) within conduits and at springs in the karstic Quintana Roo STE1,6 to continuous records of at least one year. These instrumental observations will include flow, ocean forcing, and tidal variations, as well as wind, rain, and photosynthetically active radiation to assess photosynthetic oxygen production (currently measured at Universidad Nacional Autónoma de México (UNAM) in Puerto Morelos). Prior to installing the spring instruments, we will commission a group of certified cave divers to explore and map the cave systems, including the cave that sources Pargos Spring where we have studied the first 12 m of the entrance (Fig. 3a,b). A vertical portion of the conduit will be instrumented with a Teledyne Sentinel V, which records current profiles with 5 acoustic beams (one measures vertical velocities directly) at a resolution of 0.3 m, thereby providing the first flow-rate and profile measurements within conduits. All instruments will record data every 10 minutes. The long-term deployments will require collaborations with our Mexican colleagues who have ready access to the field area (see letters of collaboration). Our colleagues will maintain the instruments every 2 months to minimize biofouling effects. To establish thresholds of forcing conditions, the cave divers will obtain profiles of salinity, DO, and pH from the surface as far into the conduit as they can safely reach. Data collection rates will be 5 Hz throughout a syzygy tidal cycle to maximize the potential of observing discharge and backflow1. These data will provide information on the threshold for when discharge and backflow shift and how this shift alters water compositions from which we can infer biogeochemical reactions.

(2) Water compositional changes linked to hydrodynamics. Flow variations mix fresh and salt water, thereby impacting organic carbon (OC) remineralization and the cascade of redox reactions (e.g., denitrification, metal and sulfate reduction, methanogenesis) that control microbial and chemical variations in STEs. Fresh and salt water end-members have variable and differing OC concentrations and labilities14, further enhancing hydrodynamic controls on chemical and microbial compositions of the STEs. The biogeochemical changes will be

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compared with data collected using in situ sensors and from water grab samples at high temporal resolution in the Quintana Roo STE and across various time and space scales in the Florida STE to assess impacts of changing head gradients on reactions within the STEs.

At the Quintana Roo STE, various in situ chemical sensors (described below) for DO, pH, nitrate, DOC, and hydrogen sulfide (H2S) will be coupled with the Sentinel V installed in conduits. These sensors will provide high temporal resolution information about changes in redox conditions of the conduits and allow estimates of fluxes of the solutes when coupled with flow rates. These logged data will be complemented with water samples collected at high spatiotemporal resolution over multiple tidal cycles; both data sets will be compared with flow data. Water will be pumped with peristaltic pumps from tubes installed in the explored conduits to a boat where it will be analyzed in the field for ephemeral solutes including Fe(II) and H2S; other samples will be preserved for lab analyses. Chemical compositions to be measured in the laboratory include components affected by organic carbon remineralization such as various N species (NO3, NH4, N2O, N2), P, total Fe and Mn. Major element concentrations (Cl, SO4, Na, K, Mg, Ca) will be used in thermodynamic modeling (PHREEQc) of mineral stabilities to estimate changes in P compositions related to calcite diagenesis91. In addition, U concentrations and 234U/238U isotope ratios will be measured to compare with the U content of fossil corals. Analytical techniques are described in Section IV.C.2.

Groundwater will also be sampled from cenotes (inland karst windows) that provide a continuum of fresh to saline groundwater across haloclines92-96 and the inland end-member for discharge to the STE. Cenotes also provide a static analogue to biogeochemical processes resulting from dynamic exchange at fresh water-saltwater mixing zones inat offshore springs. These reactions will be assessed through sampling at high spatial resolution across the halocline for OC concentrations and lability, nutrients, and microbial populations. These samples will also provide evidence for effects of wastewater disposal below the fresh water lens, a common practice that contributes organic matter, nutrients, organic pollutants, and harmful pathogens to fresh water and coastal waters97. We have found preliminary evidence for wastewater contamination in elevated NH4 concentrations, OC characteristics typical of sewage, and pathogenic microbes9. Cenotes will be instrumented with CTDs to observe tidal propagation inland and assess connectivity between the aquifer and ocean98,99.

At Indian River Lagoon, one seepage face now has more than a decade of intermittent observations (e.g., Fig. 5) of distribution of fresh and salt water from samples collected from previously installed multi-level piezometers100 that show flow rates have slowed and the position of the salt water-fresh water boundary has shifted landward through time12,101. This project will add at least 4 years of observations, which would constitute a unique and important time series for a granular STE characterized by long-term responses to sea level. Continuation of this time series, and expansion to two other sites samples as part of CS1 is important considering the recent rapid rise (~18 mm/yr) shown in tide gauges from the South Atlantic Bight13,55. Field and laboratory analyses from all three seepage faces will include identical analyses those at Quintana Roo described above.

(3) Paleo reconstructions. Our observations of modern chemistry gradients between fresh and salt water in this region will be compared with chemical data collected for objective 1 to assess potential past changes in water chemistry and quality. We will combine age data of the corals, with evidence of past changes in lagoon salinity based on the isotope and trace element geochemistry of the corals when sediment-tolerant species appeared in the reef facies at Xcaret, indicating times of high sediment fluxes and rapid sea-level rise. Trace element and isotope

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ratios of certain elements in corals have been extensively used as effective proxies to reconstruct variables such as temperature, salinity, pH, and sediment influx. (REFS). Linked observations of modern water compositions and reconstructions of paleo water compositions should thus aid our interpretations of the geochemical signals preserved in the coral skeleton.

C. Objective 3: Determine effects of thresholds on microbes, fluxes, and water resourcesMicrobial communities and chemical compositions of water will be altered as mixing

processes change at various sea levels, thereby impacting resources required by coastal human communities. Tasks within objective 3 thus include detailed and coupled laboratory analyses of time-series and synoptic water and microbial samples to assess the role of sea level on magnitudes of changes, and to apply that understanding to analyses of coastal human community responses to those changes.

(1) Water chemistry and microbes. Linked biogeochemical reactions depend on the lability of OC and available terminal electron acceptors. Lability will be determined through fluorescent techniques including 3D excitation-emission matrices to characterize dominant colored dissolved organic matter (CDOM) fractions. UV absorbance will also be collected with a Submersible Ultra-violet Nitrate Analyzer (SUNA) connected to the outlet end of the sampling tubes during in situ sampling of water in the Florida and Quintana Roo STEs, and by installing a SUNA at the location of the Sentinel V in conduits in Quintana Roo14. The SUNA collects UV absorbance at rates 0.5 Hz over wavelengths ranging from 190 to 370 nm at 0.8 nm intervals. The SUNA signal will be de-convolved by the slope ratio method102 to determine concentrations of nitrate, sulfide, CDOM and character of the OC. Real-time sampling capabilities of the instrument will allow identification of changes in solute concentrations at high temporal resolution (intra-tidal) in Quintana Roo and at small spatial resolution (10s of meters) across the Florida STE (Fig. 3).

Organic carbon analyses will be compared with microbial communities that will be characterized via DNA analysis in the Quintana Roo STE and across the seepage face in the Florida STE. Specific functional genes of interest will include those that control nitrogen cycling (e.g., nifH, nirS/nirK, nrfA, amoA), and genes characteristic of P acquisition (phoX, phoD). In addition, concentrations and distributions of genes encoding aromatic oxygenases (e.g., catechol dioxygenases and monooxygenases) will be determined to test hypotheses related to aromaticity (related to lability) of available carbon from terrestrial and marine sources. In addition to analyses of specific functional genes, the compositions of microbial communities will be characterized via high throughput sequencing of 16S rRNA genes103. Detailed information on the structures of microbial communities will provide critical information on potential shifts in community function, how these relate to the changes in OC characteristics, and link back to thresholds in sea-level change.

Similar analyses of microbial communities will be conducted on sediment cores and samples collected from the Quintana Roo and Florida STEs because of the important control of mineral surfaces on the distribution of microbes. These microbial analyses will include analysis of the distribution of the functional genes and characterization of community structures via 16S rRNA gene sequence analysis. In addition to enumeration of the functional genes, enumeration of mRNAs transcribed from those genes (via RT-qPCR) will provide indicators of in situ activities7,104. The cores will be characterized to determine distribution of reactive P pools105.

Cores will also be collected to perform flow-through experiments to modulate inputs of salt and various nutrients, and observe responses of microbial communities and their controls on

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solute compositions. The cores will be used to sequentially inject increasingly saline water (fresh to sea water salinity) through the cores. The effluent will be sampled until steady state is reached106 and used to track changes in the concentrations and activities of chemical compositions similar to the natural samples, as well as functional genes, nutrient concentrations and transformations, and organic carbon processing. These experiments should allow evaluations of the threshold changes in water compositions and microbial responses to salt content that may be compared with similar in situ field observations.

(2) Method details. Water analyses in the field and lab will be accomplished using available instrumentation at the University of Florida (see Facilities, Equipment, and Other Resources document). Precision and accuracy of water chemistry will be evaluated based on change balance errors of the major elements, duplicate analyses measured at a rate of ~10% of the samples, and replicate measurements of internal standards.

For isolation of DNA from water samples, the Power Water DNA isolation kit (MoBio, Inc.) will be used. In brief, 5 L aliquots of water from selected depths will be passed through 0.22 m Sterivex filters and preserved on ice in the field. Once in the lab, filters will be kept at 4oC until processed. For isolation of DNA and RNA from sediment samples, samples will be frozen on dry ice in the field and transported frozen to the lab. Nucleic acids will be isolated via either the MoBio Power Soil DNA or RNA isolation kit, as appropriate.

Established methods7 will allow qPCR (enumeration of genes) and RT-qPCR (enumeration of mRNAs) of the functional genes nifH, nirK, nirS, phoX, phoD, xylE. Quality of qPCR will be judged by inspection of the melt curves following PCR and assessing the efficiency of amplification. Functional gene information will be related to geochemical parameters via multivariate approaches. Metagenomic analysis of 16S rRNA genes will be conducted at the University of Florida’s Interdisciplinary Center for Biotechnological Research via sequencing on the Illumina Hi-Seq platform, and sequences analyzed via the Qiime workflow103. The Ogram lab has experience with metagenomic analysis using Qiime8.

(3) Effects on coastal human communities and human responses. Human responses will be studied to determine ways and optimal timing to adapt to sea-level rise and increased fresh water stresses2,3. We will first study the optimal land-use allocation under constraint of the fresh water carrying capacity based on potential sea-level rise rates to be determined and the water usage rate to be compiled for different land-use types in the existing land-use zoning system. We will then calculate optimal time to implement adaptation measures by calculating changing levels of water supply and demand and costs and benefits of implementing adaptation measures in different time periods. The goal is to find thresholds where water consumptions from human activities will peak and the optimal time for implementing adaptations. A behavior study will also be conducted to estimate residents’ responses and possible behavioral changes when the fresh water carrying capacity and economic impacts of adaptation measures are presented. This study will shed light on the future impacts of human activities on sustainability of water resources in coastal areas, and what needs to be done to change people’s behaviors. The results will be useful to local community managers setting policy regarding human community responses to coastal water resources.

D. Objective 4: Evaluating effects of hydrodynamic characteristics on thresholdsResponses of coastal water systems and human adaptations to sea-level change,

regardless of rates and time scales, will depend on hydraulic conductivity of the systems. Systems with high permeability, exemplified by the Quintana Roo karst systems, may respond at

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rates shorter than tidal, but certainly as short as tidal, as shown by alternating discharge and backflow at Pargos Spring (Fig. 4)1,6. In contrast, diffuse systems with low hydraulic conductivity, exemplified by the Indian River Lagoon STE, will respond more slowly to changes in sea-level rise than karst systems12. Although Indian River Lagoon is microtidal and thus shows little effect of tidal variations such as in other well-studied STEs107-110 that contain an upper saline plume111,112, it provides an important opportunity to observe physicochemical responses to sea-level change in an STE at rates longer than tidal (e.g., Fig. 5). The rates at which STEs respond to sea-level change, particularly biogeochemical reactions, water compositions, and rates of salinization, and thus sustainability of water resources, and human habitability of coastal zones in both systems depend on the response rates. Comparisons between our two study sites should thus improve our understanding of how varying hydrogeologic properties may affect characteristics of the STEs as thresholds of sea level and water use are passed. Tasks for objective 4 thus include comparisons of observations, especially flow dynamics, biogeochemical reactions, and human responses, at both study sites as accomplished in objectives 1 – 3 to evaluate the interrelations of these primary variables.

E. Summary: Relevance to Sustainability of Coastal Systems This project integrates natural and human processes related to sustainability of coastal

water resources by focusing observations, experiments, and models at two distinct end-member STEs. This topic is highly relevant to sustainability of coastal systems in general and specifically to the Coastal SEES program’s focus of understanding reciprocal feedbacks between humans and the natural environment. Feedbacks are particularly strong in coastal zones where water resources are a critical need for human habitation, but are susceptible to degradation and loss as thresholds of usage and sea level are crossed. Through our simultaneous interdisciplinary observations, experiments, and models, we expect to develop generalizable theoretical advances in natural sciences to be integrated with key aspects of human processes required to address issues of coastal sustainability.

V. Broader ImpactsBroader impacts of this work fall into several categories: human resources, intellectual

capacity building, support of site-specific coastal management, and public outreach. In terms of human resources, this project will enhance University of Florida’s growing community of interdisciplinary scholars’ ability to develop a workforce who will be able to address complex issues of sustainability in coastal environments. We will train at least five PhD students and eight undergraduate students by continuing the successes of CS1 in preparing students to identify significant scientific questions within their disciplines and relate them to collaborative disciplines. These skills will be developed in an international science setting through proposal preparation (e.g., this one) and continued with data collection and analyses, including writing papers for the peer-reviewed literature. Work proposed here will be incorporated into the PIs’ graduate level classes “Surface and Groundwater Interactions”, “Data Analysis”, and “Estuarine Hydrodynamics”. We plan to develop our bi-weekly meetings (see description in Project Management and Integration Plan) into a formal seminar focused on coastal water resource issues open to the UF community.

Our group is strengthening intellectual capacity at UF focused on coastal issues. Many UF faculty are involved in coastal science research and teaching, and our group represents a core of this larger community. Another core exists within ecological and biological sciences, and with

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Martin as co-PI, has submitted an NSF Research Traineeship (NRT) grant (NRT: HERMES: Holistic Environmental Research Model for Educating Scientists). The NRT project, if funded, supports training students in environmental research using coastal systems as a focus, but offers few research opportunities, a gap that would be filled by this project. Should both projects be funded, the two core groups would integrate through on-campus meetings, field activities, and seminars. This integration will be enhanced through management by Dr. Carol Lippincott, a Research Coordinator at the UF Water Institute. The Water Institute currently supports our work with the WIGF (see Project Management and Integration Plan). The WIGF cohort is currently involved in developing a session for the upcoming biennial Water Institute symposium (Trends, Cycles and Extreme Events) in February 2016, which has one topical focus on causes and effects of sea-level rise.

Finally, this project provides site-specific outreach in several ways. We intend to continue our collaboration with the St. Johns River Water Management District to support their efforts to build a predictive model of causes of a recent algal “superbloom” in Indian River Lagoon (see letter of collaboration). This 9-month bloom occurred in 2011 and covered about 3 to 4 times more area and contained chlorophyll-a concentrations about 6 to 7 times higher than previous blooms, and corresponded with die-off of 87% of seagrass. Causes of these algal blooms are unknown, although they correspond with increased sea-level rise rates in the South Atlantic Bight 13,55,57, suggesting linkages to nutrient inputs and/or variations in exchange with groundwater and the ocean. We will provide magnitudes and sources of benthic nutrients to aid nutrient model development (to be completed 2017) and implementation. We will also work with the Southeast Florida Regional Planning Commission to evaluate its land use and zoning practices to adapt to sea-level rise and increased water resources stress. The objective of this collaboration will be to mitigate vulnerabilities identified in this study.

We will provide outreach at two facilities in Quintana Roo, one at Rio Secreto and the other at UNAM (see letters of collaboration). Rio Secreto is a park with a focus on eco-tourism of partially water- and air-filled caves with magnificent speleothems. We have a good working relationship with personnel at the park, who have provided permission to sample the speleothems, water, and install CTDs to monitor water levels. We have presented preliminary results of work accomplished in CS1 to the cave guides, who are interested in cave formation processes and sea level variations. We intend to use this project to formalize our relationship by offering symposium to the guides, including information valuable to their tours and other audiences (see letter of collaboration). We also intend to teach short courses at the UNAM facility at Puerto Morelos, a field station providing logistical support (e.g., dock facilities; dive locker and gear; electronic and geochemical laboratories) for our operations in Quintana Roo (see letter of collaboration). These short courses will be pitched at upper level undergraduate/graduate students, focused on questions in this proposal. In addition, we have and will continue to present seminars, aimed at the students and faculty, describing our work and results. To develop a meaningful exchange we will host Mexican colleagues at UF for seminars, project discussions and manuscript development.

VI. Research team and integrationThe assembled research team is exceptionally well suited to address the proposed tasks.

Through CS1, we have worked collaboratively on coastal water resource and sea-level change problems for the past two years, including multiple field trips to Quintana Roo and the east coast of Florida. Preliminary results from CS1 are now being presented in peer-reviewed

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literature1,5,6,13,89. These results have also led us to develop the project proposed here, which our CS1 experiences will allow us to quickly initiate. Our team includes a wide range of disciplines, some of which have rarely collaborated in the past. Our team has now been fully integrated through our biweekly meetings and field trips during which we educated participants in important disciplinary questions and innovative methods for addressing sea-level rise issues. We will continue to develop those interdisciplinary ties as described fully in the attached Project Management and Integration Plan.

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