Influence of fisheries and shoreline management on limnological characteristics of three Missouri reservoirs

ABSTRACT

Landscape-level analyses based on land cover, morphology, and hydrology account for most of the cross-system variation in pelagic nutrients and suspended solids in Missouri reservoirs. They are based on geometric means, which reduce the influence of extreme temporal variation measured in individual reservoirs. This analysis of 3 conservation reservoirs, managed to benefit recreational fisheries, details how internal processes can alter nutrients, chlorophyll, mineral turbidity, and transparency in long-term (21–42 year) datasets, which contribute to temporal variation. Management practices include the addition of grass carp and herbicides to control nuisance macrophytes and shoreline stabilization with rock and water willow. Among these reservoirs, there is strong evidence that macrophyte removal can increase pelagic nutrients by >90%, resulting in a switch to plankton-dominated conditions (alternative states). In one case, eradication of aquatic vegetation increased mineral turbidity by >60%, which was reversed by reestablishing macrophytes and stabilizing the shoreline. This temporal series supports the modifications of phytoplankton–nutrient relations by mineral turbidity shown in state-wide analyses. Collectively, the long-term data show a significant increase in cyanobacteria biovolume and cyanotoxins, with maximum microcystin concentrations increasing as much as 20 times. Actively flipping lakes to plankton-dominated systems via fisheries management and shoreline stabilization practices has negative impacts on overall water quality, with implications for human and wildlife health.

KEYWORDS:

• chlorophyll
• cyanobacterial harmful algal blooms
• glyphosate
• grass carp
• microcystin
• trophic status

Acknowledgements

We acknowledge the Missouri Department of Natural Resources, which funds the Missouri Statewide Lake Assessment Program (SLAP) coordinated by the University of Missouri (MU) Limnology Laboratory. We thank Dr. Alba Argerich and Anthony Thorpe for data management, as well as all the MU Limnology Laboratory employees who contributed to sample collection and analysis, particularly Carol Pollard. We thank the fishery managers at MDC for detailing the scope and timing of their management efforts.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the US Environmental Protection Agency and the Missouri Department of Natural Resources.