Files
Abstract
Nitrate pollution has become one of the most prevalent causes of water quality degradation globally due to increasing anthropogenic input from suburban and agricultural runoff, municipal wastewater, and industrial waste. Freshwater mussel populations have been declining globally for decades at an alarming rate. Pollution is one of many factors implicated for contributing to these declines, but limited data have directly linked toxicants to mussel population effects. The effects of nitrate exposure are largely unknown for freshwater mussels, particularly during the parasitic stage of their complex lifecycle. Additionally, toxicity testing with fish is often limited to a few model species, such as fathead minnows (Pimephales promelas), but relatively little is known about how representative model species are of more ecologically relevant (e.g. imperiled) species. Therefore, I addressed the following objectives to better evaluate the risk of nitrate to freshwater mussels and fish: 1) evaluate the acute toxicity of nitrate to multiple species of common and imperiled freshwater mussels and fish; 2) determine if nitrate exposure at different stages could alter the ability of glochidia to attach to host fish and metamorphose to the juvenile stage; and 3) use matrix population models to project the potential effects of nitrate on freshwater mussel populations. To achieve these objectives, I utilized standardized toxicity testing methods, partial life-cycle assessment, and population modeling with freshwater mussels and standardized toxicity testing with larval fish. Acute test results did not indicate a risk posed to freshwater mussel glochidia or fish with current environmental nitrate levels, but partial life-cycle tests revealed a significant effect on freshwater mussel juvenile production not distinguishable by other test methods. Matrix population models allowed us to project nitrate effects on mussel population viability and indicated the potential for substantial population declines from nitrate exposure at different mussel life stages. Through the studies described here I present a more complete description of the potential impacts of nitrate on freshwater mussel populations. Data are still needed to fully understand the risk to mussels and implications, but these studies are useful for conservationists, managers, and regulators to begin establishing the role of nitrate in freshwater mussel declines.