Entwurf eines Vorschlags für ein integratives College-Projekt

Topic: The Impact of Microplastics on Freshwater Benthic Macroinvertebrate Communities: A Comparative Analysis of Urban and Rural Streams Outline: I. Introduction (Title, Description, and Significance) II. Literature Review (Sources on microplastic prevalence, effects on aquatic life, and biomonitoring) III. Research Gaps (Lack of comparative field studies, limited focus on benthic macroinvertebrates, and absence of standardized metrics) IV. Research Question and Objectives V. Proposed Methodology (Site selection, sampling, laboratory analysis, and statistical approach) VI. Expected Contributions VII. References --- **Integrative Project Proposal: Microplastics and Freshwater Benthic Macroinvertebrates** **1. Title and Description** **Title:** The Impact of Microplastics on Freshwater Benthic Macroinvertebrate Communities: A Comparative Analysis of Urban and Rural Streams **Description:** This Integrative Project (IP) proposes a field-based comparative study to assess the abundance and diversity of benthic macroinvertebrate communities in relation to microplastic contamination in urban and rural stream ecosystems. The project will integrate principles from ecology, environmental chemistry, and hydrology to quantify microplastic concentrations in sediment and water, and correlate these with macroinvertebrate community metrics (e.g., richness, evenness, and pollution tolerance indices). By comparing streams with contrasting land-use contexts, this research aims to elucidate the potential ecological consequences of microplastic pollution on freshwater benthic fauna. **2. Literature Overview** The pervasive presence of microplastics (particles < 5 mm) in aquatic environments has become a focal point of environmental research. Initial studies have documented their global distribution, from marine sediments to remote freshwater systems (Eerkes-Medrano et al., 2015). In freshwater ecosystems, microplastics originate from diverse sources, including wastewater treatment effluent, urban runoff, and the fragmentation of larger plastic debris (Horton et al., 2017). These particles are not inert; they can adsorb persistent organic pollutants and heavy metals, potentially increasing their toxicity to biota (Bakir et al., 2014). The ecological impacts on aquatic organisms are concerning. Laboratory studies have demonstrated that microplastic ingestion can cause physical blockages, reduced feeding, and inflammatory responses in various species (Wright et al., 2013). For benthic macroinvertebrates, which are crucial for nutrient cycling and serve as a primary food source for higher trophic levels, exposure to microplastics can lead to reduced growth and reproductive success (Redondo-Hasselerharm et al., 2018). Furthermore, these organisms are widely used as bioindicators in stream health assessments due to their differential sensitivities to pollutants (Barbour et al., 1999). However, most ecotoxicological studies are conducted under controlled laboratory conditions, which may not accurately reflect the complex interactions and environmental factors present in natural streams. **3. Research Gaps** Despite the growing body of literature, significant gaps remain. First, there is a scarcity of comparative field studies that directly link microplastic contamination to benthic macroinvertebrate community structure in natural settings. Most research has focused on marine environments or single-species laboratory exposures. Second, the influence of land use (e.g., urban vs. rural) on the relationship between microplastics and benthic communities is poorly understood. Urban streams are likely to have higher microplastic loads, but the direct ecological consequences relative to rural counterparts are not well quantified. Third, there is a lack of standardized metrics for assessing microplastic risk in biomonitoring programs. Traditional indices like the Hilsenhoff Biotic Index (HBI) or Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness have not been systematically integrated with microplastic contamination data. This project aims to address these gaps by providing empirical field data that links microplastic pollution to benthic community health across a land-use gradient. **4. Research Question** The central research question guiding this project is: **How does the concentration and composition of microplastics in stream sediments correlate with the diversity and composition of benthic macroinvertebrate communities, and does this relationship differ between urban and rural streams?** To answer this, the project will pursue the following objectives: (1) Quantify and characterize microplastic particles (type, size, and polymer) in sediment samples from selected urban and rural streams; (2) Assess benthic macroinvertebrate community structure using standard collection and identification protocols; (3) Calculate biological indices (e.g., EPT richness, HBI) and correlate them with microplastic concentrations; and (4) Compare the observed patterns between urban and rural sites to identify potential land-use-specific impacts. **5. Contributions** This project is significant for several reasons. From a scientific perspective, it will provide much-needed empirical evidence on the ecological impacts of microplastics in freshwater benthic environments, moving beyond laboratory-based predictions. The comparative urban-rural design will help isolate the effects of microplastics from other confounding stressors (e.g., nutrient pollution, habitat degradation) that are common in urban streams. From a practical standpoint, the findings could inform the development of microplastic-specific metrics for inclusion in existing biomonitoring frameworks, enhancing the ability of environmental agencies to assess and manage the risks of this emerging contaminant. Finally, the project will contribute to public awareness and policy discussions regarding plastic waste management and its impact on local water resources. **6. Methods** To address the research question, a comparative field study will be conducted over a single sampling season (spring) to minimize temporal variability. Six streams will be selected: three with predominantly urban watersheds and three with predominantly rural/agricultural watersheds, based on land-use data from GIS. At each stream, three replicate sampling sites will be established, spaced 100 meters apart. **Sediment and Microplastic Analysis:** At each site, sediment samples will be collected using a stainless-steel grab sampler from depositional zones. In the laboratory, microplastics will be extracted using density separation with a sodium chloride solution and subsequent filtration. Particles will be visually identified and categorized by shape (fiber, fragment, film) under a dissecting microscope, with a subset analyzed using Fourier-transform infrared spectroscopy (FTIR) to confirm polymer types. Microplastic concentration will be expressed as particles per kilogram of dry sediment. **Macroinvertebrate Sampling:** Benthic macroinvertebrates will be collected using a Surber sampler (500 µm mesh) from riffle habitats. Samples will be preserved in 70% ethanol and later sorted and identified to the family level in the laboratory. Community metrics, including total abundance, taxa richness, EPT richness, and the Hilsenhoff Biotic Index, will be calculated for each site. **Statistical Analysis:** Data will be analyzed using a combination of descriptive and inferential statistics. A t-test or Mann-Whitney U test will be used to compare microplastic concentrations and macroinvertebrate metrics between urban and rural streams. Pearson or Spearman correlation analyses will be performed to assess the relationship between microplastic concentration and biological indices. Finally, a multiple regression model will be used to account for potential confounding variables (e.g., water quality parameters like dissolved oxygen and temperature). All statistical analyses will be conducted using R software. This methodology is designed to provide a robust, quantitative assessment of the relationship between microplastics and benthic community health, directly answering the proposed research question. **7. References** Bakir, A., Rowland, S. J., & Thompson, R. C. (2014). Enhanced desorption of persistent organic pollutants from microplastics under simulated physiological conditions. *Environmental Pollution*, 185, 16-23. Barbour, M. T., Gerritsen, J., Snyder, B. D., & Stribling, J. B. (1999). *Rapid bioassessment protocols for use in streams and wadeable rivers: Periphyton, benthic macroinvertebrates and fish* (2nd ed.). U.S. Environmental Protection Agency. Eerkes-Medrano, D., Thompson, R. C., & Aldridge, D. C. (2015). Microplastics in freshwater systems: A review of the emerging threats, identification of knowledge gaps and prioritisation of research needs. *Water Research*, 75, 63-82. Horton, A. A., Svendsen, C., Williams, R. J., Spurgeon, D. J., & Lahive, E. (2017). Large microplastic particles in sediments of tributaries of the River Thames, UK – Abundance, sources and methods for effective quantification. *Environmental Pollution*, 220, 540-548. Redondo-Hasselerharm, P. E., Falahudin, D., Peeters, E. T. H. M., & Koelmans, A. A. (2018). Microplastic effect thresholds for freshwater benthic macroinvertebrates. *Environmental Science & Technology*, 52(4), 2278-2286. Wright, S. L., Thompson, R. C., & Galloway, T. S. (2013). The physical impacts of microplastics on marine organisms: A review. *Environmental Pollution*, 178, 483-492.

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