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Access Type

WSU Access

Date of Award

January 2025

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Biological Sciences

First Advisor

Donna R. Kashian

Abstract

Benthic macroinvertebrates are critical bioindicators that are sensitive to a range of environmental stressors, such as urbanization, nutrient enrichment, and salinization. These stressors can lead to shifts in community composition and a subsequent decline in ecosystem health, jeopardizing the integrity of fluvial systems. In this study, land use settings were compared with publicly available nitrogen (N) and phosphorus (P) data and integrated with benthic macroinvertebrate surveys to assess the impact of nutrient conditions on Michigan waterways over a 20-year period (2002-2021). This analysis aimed to explore how different land use settings influence the seasonal and annual concentrations of N and P in Michigan streams and how these nutrient levels affect benthic macroinvertebrate communities. Next, in-situ assessments of benthic macroinvertebrates were performed at twenty streams to evaluate community responses in response to available basal resources and riparian cover, using a watershed-scale land cover analysis. This study compared two distinct climate types: humid continental (southeastern Michigan) and tropical monsoonal (Puerto Rico). The focus was on sites impacted by development and agricultural land use, as well as those with varying riparian cover densities. This comparison allowed for an assessment of how anthropogenic disturbances and riparian cover affect benthic macroinvertebrate communities, considering their different roles in each climate effects. Under controlled experimental conditions, burrowing mayfly nymphs (Hexagenia spp.), were exposed to road salt to examine the effects of salinity on their behavior, physiology, feeding strategies and nutrient assimilation. Hexagenia spp. are commonly used in toxicity studies due to their presence being indicative of good water quality and/or habitat recovery. The study evaluated several parameters, including isotopic signatures (13C and 15N), survival rate, drift, and respiration responses across various experimental designs.

The main findings indicate that increased agricultural and developed land uses promote a rise of inorganic nitrogen (NO2 + NO3) and TP, which, in turn, drive changes in benthic macroinvertebrate communities. However, nutrients do not appear to be strongly correlated with land use and shifts in these communities at a state-level. Agricultural and land development disturbances result in the prevalence of more tolerant species assemblages, and more collectors-gatherers (e.g., chironomids and oligochaetes). Conductivity influences these assemblages, while riparian cover and higher drainage areas serve as less resilient features in temperate regions, although they are more resilient in tropical regions. Shifts in feeding strategies and respiration in Hexagenia suggest signs of recovery in freshwater systems, linked to increased tolerance of CaCl2 + Mg. This research highlights the importance of promoting the restoration and management of fluvial systems through three key actions: (1) identifying areas in need of stream assessment in Michigan, USA, (2) understanding how climate effects influence benthic macroinvertebrate assemblages in areas with similar riparian cover and anthropogenic disturbances, and (3) raising awareness about the harmful impacts of salt application, which adversely affects key bioindicators and triggers a cascade of effects throughout food web interactions.

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