Water Resources Research Act Program

Details for Project ID 2017MN388B

Assessing the role of buffer strips in nutrient and organic matter export and mitigation of harmful algal blooms

Institute: Minnesota
Year Established: 2017 Start Date: 2017-03-01 End Date: 2019-02-28
Total Federal Funds: $29,701 Total Non-Federal Funds: $59,404

Principal Investigators: James Cotner

Project Summary: Minnesotans and many other parts of the nation and world benefit from our incredibly productive agricultural industry, but we also realize important costs that are becoming more and more apparent. Despite numerous attempts to limit the transport of nutrients into freshwater systems, nutrient pollution remains a major issue in Minnesota. Nearly a third of the water bodies listed on the 2014 impaired waters inventory in MN have nutrient pollution as their primary impairment. In 2015, Minnesota enacted a new law requiring the installation of vegetative buffer strips along the boundaries of all public waters and public drainage systems by 2018 to limit the transport of nutrients from the land into aquatic systems. Installation of these buffer strips requires a shift in land use practices, particularly in high agricultural areas. There have been a number of studies that have attempted to quantify the nutrient removal efficiency of buffer strips, but very few studies have examined how buffer strips impact the composition and reactivity of nutrients that do get transported to nearby streams and lakes. Organic matter reactivity controls the extent to which organic nutrients will increase biological oxygen demand, decrease dissolved oxygen, and increase phosphorus and nitrogen loading to aquatic systems. Furthermore, the composition of nutrient pools (not just the total quantity of nutrients) can impact the formation of harmful algal blooms (HABs), which degrade water quality in eutrophic systems. Therefore, this proposal aims to advance the scientific understanding of how changes in land use practices, i.e., the installation of buffer strips) impact the transport of nutrients across the land-aquatic boundary. This work will provide novel understanding of the effectiveness of buffer strips in controlling eutrophication in aquatic systems. Here, we will determine: (1) how buffer strips affect the composition and quantity of nutrients exported to aquatic systems; (2) how buffer strips affect the reactivity of dissolved organic matter exported to aquatic systems; and (3) how buffer strips affect the composition of the phytoplankton and bacterial communities in nearby aquatic systems. We hypothesize that: (1) non-buffered agricultural systems should export a higher proportion of nutrients in inorganic, rather than organic forms relative to buffered systems; (2) mean nutrient bioavailability should decrease when buffer zones are present due to transformation of inorganic nutrients into less reactive organic forms; and (3) buffer strips should shift the balance of production toward heterotrophic organisms in downstream aquatic habitats due to a shift toward organic rather than inorganic nutrients. This work will combine intensive field studies and controlled laboratory experiments to explore these objectives. We will combine high resolution chemical and genetic data with functional biological assays to link organic matter composition with ecosystem function. Ten study systems in agricultural regions of Minnesota will be chosen based on the intensity of buffer strips within their watersheds. We will sample the lakes and inflow tributaries in these watersheds to capture the effect of buffer strips on both initial export of organic matter and on downstream systems. Microbial and phytoplankton community composition and diversity will be assessed using a high throughput targeted gene marker survey of 16S and 18S rRNA. Composition of the DOM pool will be assessed using two approaches: rapid optical characterization using spectrofluorometric methods and molecular characterization using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Lability of the DOM will be assessed using a high throughput bio-assay, where nutrient lability is quantified using a biomass response of the bacterial or phytoplankton community. The work proposed will facilitate the development of several early career scientists (undergraduates, graduate students, and a post-doctoral fellow) and will be coordinated with a science in the schools (K-8) in the Twin Cities. Buffer strips have been shown to be effective traps for inorganic nutrients, but little is known about the composition and reactivity of organic matter that is transported through these zones. By addressing this gap, we will increase the scientific understanding of how buffer strips modify the nutrients transported into aquatic systems with the potential to improve management practices. Our work will determine how planktonic communities are affected by buffer strips, evaluate the potential for effects on HABs, and describe potential feedbacks that could either enhance or limit the ability of buffer strips to lessen the impacts of eutrophication.