PS 37-27 - CANCELLED - Contextualizing long-term effects of land use on nutrient pollution, and impacts on benthic macroinvertebrate assemblages in Michigan streams (USA)
Abstract: Nutrient pollution negatively affects stream biota, water quality, and aquatic industries such as tourism and water treatment. Many of these impacts come at an economic cost. Despite management efforts to improve water quality, excess nitrogen (N) and phosphorus (P) constituents have steadily increased because of agricultural inputs, deforestation, human population growth, and urbanization. Benthic macroinvertebrate metrics are often used in water quality monitoring as indicators of stream health due to their wide range of pollution tolerance among taxa. Here we examined long-term median concentrations of nutrients (i.e., TN, TKN, NO2, NO3, NH3, NH4, and TP) and relationships between land use and benthic macroinvertebrate metrics, including diversity and feeding guilds, to determine how land use settings affect nutrient concentrations and macroinvertebrate composition in Michigan (USA) streams. Records between 2022-2021 were retrieved from multiple agencies in the Water Quality Portal, synthesized, and partitioned into developed and agricultural (with > 45% dominance), undeveloped (with ≤ 5% of urban and ≤ 25% agricultural dominance), and mixed land use (all combined); and percent of developed/agricultural land-cover (0-10%, 10-20%, 20-30%, 30-40%, >40%).
Statewide, median concentrations of TN ranged between 0.53-1.44 mg/L, with no marked differences among land use, and TP ranged between 0.03-0.09 mg/L from developed/agricultural sites. A significant change in nutrient concentrations occurred once it reached 30-40% of combined land use, where inorganic nitrogen and ammonia concentrations were two to ten times higher than in undeveloped areas. Collector-gatherers were the dominant macroinvertebrate field guild overall. However, highly polluted sites had fewer collector-filterers and more predators, likely associated with higher secondary production that could be stimulated by land disturbance. Identifying nutrient-impaired streams could focus and improve management efforts leading to improved habitat restoration. Additionally, the research can provide information on the role of benthic macroinvertebrates in nutrient cycling in streams.
