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Investigating Vernal Pool Quality to Inform Restoration and Conservation Efforts

Leah Nagel

SUNY College of Environmental Science and Forestry

Final Report for the Edna Bailey Sussman Foundation 2016

Background

Vernal pools are small, temporary wetlands that provide important nursery habitat for a number of threatened and endangered species while generating habitat complexity at the landscape scale. In the northeastern United States, vernal pools were the most abundant wetland type in the landscape and were present at high densities. However, vernal pools are disappearing due to inadequate regulatory protection and because they are easily destroyed. Even where pools are protected and remediation efforts are required, the hydroperiod (the length of time in which the pool is flooded) of restored pools often does not match that of natural pools. To maintain the landscape-level densities of vernal pools required to sustain vernal pool-dependent species, we must ensure that we are both prioritizing the protection of high-quality pools and that restoration efforts are creating functional vernal pool systems.

In New York State there has been substantial work conducted on vernal pools at local and regional scales; however, vernal pool distribution and biodiversity are not well described on a statewide scale. To address this, the New York Natural Heritage Program (NYNHP) received an EPA Wetlands Development grant to assess the current state of vernal pool knowledge in the state and use those data to develop a rapid-assessment protocol to assess the distribution and biodiversity in the state, and from there develop usable quality metrics to assess pools throughout the state. This summer’s fieldwork served as a pilot study for the larger NYNHP effort, and tested the feasibility of potential methods for the 2017-2018 statewide surveys.

The objectives for this summer were to 1) develop and refine a rapid-assessment protocol to measure a variety of pool characteristics including hydroperiod, water chemistry, amphibian survival, and macroinvertebrate assemblages; and 2) assist in the construction of a database that is now being used by the New York Natural Heritage Program (NYNHP) to house a statewide dataset assembled partners from around the state with existing vernal pool datasets and will be used to house data collected during statewide rapid assessment surveys in 2017-2018.

Results and Discussion

Biweekly depth surveys on 74 natural and created pools located in Tully, NY and Beaver Dams, NY were conducted between March and September 2016. Maximum depths ranged from 16cm to 57cm, and maximum pool surface areas ranged from 9m2 to 850 m2. Pools dried completely as early as April, with 8 pools drying by the end of May (Figure 1). A total of 50 pools remained continuously flooded throughout the sampling period. Surface area did not appear to impact hydroperiod; the three largest pools at the Beaver Dams site all dried by midsummer, while the largest pool in Heiberg remained close to maximum capacity through the end of the sampling period.

Figure 1. Number of pools that contained water continuously from the first sampling date through the end of each month surveyed.

To quantify the composition of vegetation structures in pools, average percent cover (to the nearest 5%) of seven vegetation parameters was recorded during multiple surveys throughout the spring and summer. Most pools were dominated by open water, with only 17 pools averaging less than 20% open water and 27% of pools remaining 100% open. Few pools contained high concentrations of aquatic plants, with only three pools containing more than 20% emergent vegetation and seven containing more than 20% submerged vegetation. Algae presence was also noted during vegetation surveys.

Water quality surveys were conducted in July for pH and dissolved oxygen. Water samples for pH were taken and measured in the lab, while dissolved oxygen levels were measured in the field using a YSI Model 85 probe early in the morning to obtain minimum dissolved oxygen levels caused by photosynthetic organisms respiring throughout the night. Pool pH ranged from 5.19 to 7.72, with an average pH of 6.45 (Table 1). Dissolved oxygen concentrations ranged from 0 to 8.83 mg/L and 0 to 98.7% saturation.

Table 1. Water quality parameters measured across all 74 pools.

pH

DO (mg/L)

%DO

Mean

6.45

0.711

7.99

Min

5.19

0.0

0.0

Max

7.72

8.83

98.7

Median

6.39

0.30

3.32

Figure 2. Dissolved oxygen levels for pools with and without algae or >20% submerged vegetation coverage. Mean %DO levels were 11.9% and 5.29% respectively; there was no significant difference between the two groups (t = -0.3385, df = 49, P = 0.18).

To test the effect of photosynthetic organisms on dissolved oxygen concentrations, I used a t-test to compare average dissolved oxygen levels between pools with and without photosynthetic organisms (algae and/or pools with >20% coverage of submerged vegetation). Pools with photosynthetic organisms had a greater range of dissolved oxygen levels (Figure 2); however, there was no significant difference in average dissolved oxygen between the two groups. This was unexpected, as waterbodies with high primary productivity often have more extreme maximum and minimum dissolved oxygen concentrations during the day and at night respectively. One explanation for this pattern can be taken from the two pools that had the highest levels of dissolved oxygen: both pools had relatively clear water and had very little organic material on the bottom. Many pools with no algae or macrophytes contained high levels of decomposing organic material, particularly leaf litter, which may have contributed to the low dissolved oxygen levels. Dissolved oxygen levels were low in the majority of pools sampled, and next year’s sampling will include daytime sampling to detect peak levels of dissolved oxygen and compare the differences in dissolved oxygen levels to see if photosynthetic organisms are contributing significantly to oxygen levels in the pool.

Amphibian surveys were conducted during the summer to assess the distribution and survival of amphibian species at both locations, with a focus on spotted salamanders (Ambystoma maculatum, hereafter AMMA) and wood frogs (Lithobates sylvaticus, hereafter LISY), which rely heavily on vernal pools for breeding and are especially vulnerable to predation by larger vertebrate predators. Egg mass surveys were conducted in the early spring during peak oviposition. Across all 74 pools, LISY eggs were detected in 37 pools and AMMA eggs in 53 (Table 2). Jefferson salamander egg masses (Ambystoma jeffersonianum) were only found in a single pool in the Beaver Dams site (which dried before the eggs hatched) and as a result are largely excluded from this analysis. Throughout the course of the summer, biweekly visual encounter surveys were conducted, with two additional intensive amphibian surveys using dipnets and stovepipe samplers. Between these two methods, LISY tadpoles were detected in 19 pools and AMMA larvae in 24 pools.

Table 2. Total number of pools with L. sylvaticus (LISY) and A. maculatum (AMMA) eggs and larvae.

LISY

AMMA

Egg Masses Present

37

53

Larvae Present

19

24

Larval amphibian presence was not significantly correlated with any of the variables tested. None of the habitat variables had correlations stronger than Ρ = 0.4, and the number of egg masses deposited in the spring and the presence of larvae in the pools during the summer was not strongly correlated for either species (Ρ = 0.073 and 0.455 for LISY and AMMA, respectively). The lack of relationship between egg mass counts and apparent larval survival underscores the importance of conducting amphibian surveys throughout the summer in addition to breeding effort and identifying the factors that drive survival to metamorphosis and therefore juvenile production into the larger population. Many regional assessments of vernal pools rely on egg mass counts as a proxy for pool quality, with higher egg mass counts associated with high-quality vernal pools. Based on the results of this study, larval survival must be taken into account to get an accurate estimate of a pool’s contribution to amphibian populations.

Table 3. Univariate correlations between larval amphibians observed in a given pool throughout the sampling period and explanatory variables.

Larvae Observed

Egg Mass Count

% Dissolved Oxygen

Max Depth

Min Depth

% Open

% Submerged Vegetation

LISY

0.073

-0.091

0.049

-0.136

-0.160

-0.012

AMMA

0.455

0.081

0.397

0.245

-0.231

0.276

Further Directions

In order to more accurately capture amphibian survival, next summer’s surveys will include biweekly abundance surveys for larval amphibians rather than presence alone. Further work on developing an assessment method for macroinvertebrates that is relatively rapid is also necessary; sample processing from the summer is still in progress and the method is not feasible for a truly rapid assessment. The data collected this summer will inform the methods selected for the statewide assessment protocol for 2017 and 2018.

Acknowledgements

Many thanks to my supervisor Dr. Matt Schlesinger, as well as my major professor Dr. James Gibbs, for their guidance and encouragement throughout the project. Thanks to Jim Curatolo for offering his property as a study site and allowing us to stay onsite, and to my field technicians Sahila Kudalkar, Alexandra Mulvihill, Adrian Rouse, Ryan Siless, and Stephen Sussman, whose help allowed me to accomplish far more than I would have been able to alone. Finally, this work would not have been possible without the support of the Edna Bailey Sussman Foundation, and the additional support of the Garden Club of America, the New York State Wetlands Forum, and the SUNY-ESF GSA.

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