New York State is home to more than 5,700 dams, which range from large high-head hydropower dams to small headwater impoundments (Vedachalam & Riha 2014). In small streams, dams can disconnect aquatic organisms from important refuge habitats in times of heat stress or food scarcity, and they may also degrade water quality by altering stream flow. While small dam removal can restore connectivity and health to aquatic habitats, such management actions must be planned carefully to minimize unintended impacts. For example, the removal of dams can release stored debris, sediments, and pollutants (e.g., toxic methylmercury) and can simultaneously alter the nutritional value (i.e., essential fatty acid content) of basal food sources (Huang et al. 2024). Together, these effects of removal can be detrimental to aquatic and terrestrial organisms. While research designed to anticipate effects of dam removal on ecosystem health is time-intensive, typically relying on long-term ecosystem monitoring pre- and post-removal (Tonitto & Riha 2016), we propose a rapid assessment solution. Beaver dams, which are widespread in small streams across New York State, undergo natural assembly and disassembly with changes in intensity of beaver activity over time (Ecke et al. 2017). Using a space-for-time substitution approach, we aim to use observations of this “beaver dam life cycle” to quickly understand the impacts of small dam removal on ecosystem health and function over time. In particular, we are interested in the ways in which beaver ecosystem engineers may modify the nutrition and contamination levels of insects, as food sources for higher-order terrestrial and aquatic consumers.
Sample collection was conducted in July 2024 by Co-PI Brahmstedt and PI Arsenault. We visited three streams (East Creek, Sucker Brook, and Chair Rock Creek) and sampled 10 sites above and below beaver dams spanning the beaver dam life cycle (active dam, recently breached, and recovery phase). We focused collections on predatory aquatic insects, which could be collected with sufficient biomass for total mercury, methylmercury, and fatty acid analysis. A total of 400 predatory individuals were collected from 3 orders and 9 families. Where possible, at least three insect taxa were collected per site. Sample collections were successful, with all necessary samples being collected, preserved, and stored until laboratory processing. Sample collection information and associated data were printed on data sheets and subsequently entered electronically. Co-PI Brahmstedt worked with equipment in Co-PI Razavi and PI Arsenault’s labs to prepare frozen insect samples for analysis. Samples were freeze-dried and homogenized in November and December 2024. A subset of samples was delivered to Co-PI Fernando’s lab at the Center for Air and Aquatic Resources Engineering and Science (CAARES) Another subset of samples was delivered to the Finger Lakes Institute for methylmercury analysis in April 2025, for which data was received in December 2025. A final subset of sample material was analyzed for total mercury by Co-PI Razavi (ESF), for which data was received also in December 2025. Preliminary data analysis suggests that aquatic insects may act as an ecological trap (higher polyunsaturated fatty acid content corresponded to higher total- and methylmercury content), but this heightened nutritive value and contamination load may occur in forested areas, rather than beaver impounded meadows (Figure 1a–d). This is the opposite of what we had predicted, which was that beaver-engineered habitats would be more conducive to mercury storage and food web transfer. Next, our team will begin preparing a manuscript for publication. We will also prepare two conference presentations alongside this manuscript.
References:
Ecke, F., Levanoni, O., Audet, J., et al. 2017. Environmental Research Letters, 12, 113002.
Huang, J., Guo, F., Burford, M. A., et al. 2024. Journal of Environmental Management, 355, 120501.
Tonitto, C., and Riha, S. J. 2016. Sustainable Water Resources Management 2, 489–507.
Vedachalam, S., and Riha, S. J. 2014. River Research and Applications 30, 1195–1205.