Stream Nutrients: Relationships to Fish and Benthic Assemblages in Maryland Streams

One of the most pressing environmental problems for the 21^st century is the presence of excess nutrients in aquatic ecosystems throughout the world, often resulting in ecosystem collapses, economic damages and human health concerns.  Small freshwater stream systems are not immune to nutrient loading, resulting from anthropogenic influences such as agricultural practices and runoff, wastewater discharge, atmospheric deposition, and both urban/suburban point and non-point sources.  I used the Maryland Biological Stream Survey (MBSS) database to examine nutrient and benthic macroinvertebrate data collected during the MBSS Spring Index period and fish assemblage data from the MBSS Summer Index period for Maryland.  Statistical analyses indicated that stream nutrient levels (TN, NO₃, NO₂, NH₃ and TP) minimally affect fish assemblages in first, second and third order non-tidal streams.  However, there were strong statistical relationships of nutrients to several benthic macroinvertebrate parameters, including numbers of EPT and especially Ephemeroptera numbers, with significant reductions when TN levels exceed 4-6 mg/L. Although multiple stressors are often present in Maryland streams, nutrients are an important stressor to biotic assemblages, and need consideration in conservation of intolerant Maryland fish species and stream biodiversity. BMP development and implementation for nutrient management needs acceleration in Maryland.