Relating environmental variables with aquatic community structure in an agricultural/urban coldwater stream

Daniel T L Myers,E Wendy Ogilvie,Richard R Rediske,James N Mcnair,Aaron D Parker

doi:10.1186/s13717-021-00312-6

Abstract

BackgroundUrban areas are often built along large rivers and surrounded by agricultural land. This may lead to small tributary streams that have agricultural headwaters and urbanized lower reaches. Our study objectives assessed are as follows: (1) landscape, geomorphic, and water quality variables that best explained variation in aquatic communities and their integrity in a stream system following this agricultural-to-urban land use gradient; (2) ways this land use gradient caused aquatic communities to differ from what would be expected for an idealized natural stream or other longitudinal gradients; and (3) whether the impacts of this land use gradient on aquatic communities would grow larger in a downstream direction through the agricultural and urban developments. Our study area was an impaired coldwater stream in Michigan, USA.ResultsMany factors structured the biological communities along the agricultural-to-urban land use gradient. Instream woody debris had the strongest relationship with EPT (Ephemeroptera, Plecoptera, and Trichoptera) abundance and richness and were most common in the lower, urbanized watershed. Fine streambed substrate had the strongest relationship with Diptera taxa and surface air breather macroinvertebrates and was dominant in agricultural headwaters. Fish community assemblage was influenced largely by stream flow and temperature regimes, while poor fish community integrity in lower urban reaches could be impacted by geomorphology and episodic urban pollution events. Scraping macroinvertebrates were most abundant in deforested, first-order agricultural headwaters, while EPT macroinvertebrate richness was the highest downstream of agricultural areas within the urban zone that had extensive forest buffers.ConclusionEnvironmental variables and aquatic communities would often not conform with what we would expect from an idealized natural stream. EPT richness improved downstream of agricultural areas. This shows promise for the recovery of aquatic systems using well-planned management in watersheds with this agricultural-to-urban land use pattern. Small patches of forest can be the key to conserving aquatic biodiversity in urbanized landscapes. These findings are valuable to an international audience of researchers and water resource managers who study stream systems following this common agricultural-to-urban land use gradient, the ecological communities of which may not conform with what is generally known about land use impacts to streams.

Highlights

Many large cities are located along navigable waterbodies because of historic and/or present day uses of the rivers such as commercial transport, hydroelectric production, and waste disposal (Gallup et al 1999)
We found that environmental variables and aquatic communities in the watershed were affected by longitudinal and land use gradients
For river basins following a land use pattern of agricultural headwaters to urban lower reaches, interactions of landscape, geomorphic, and water quality/pollution variables can be influential on the structure of fish and macroinvertebrate communities

Summary

Introduction

Many large cities are located along navigable waterbodies because of historic and/or present day uses of the rivers such as commercial transport, hydroelectric production, and waste disposal (Gallup et al 1999). As a result of this land use pattern of urban areas along waterbodies surrounded by agricultural lands, numerous small, tributary stream watersheds have become characterized by predominantly agricultural land use in the headwaters and urban land use in the lower reaches. Rivers and streams are known to exhibit longitudinal patterns of many physical properties including average stream width and depth, shading, velocity, and habitat characteristics Such patterns are central to the River Continuum Concept and its more recent elaborations (Vannote et al 1980; Tornwall et al 2015). Urban areas are often built along large rivers and surrounded by agricultural land This may lead to small tributary streams that have agricultural headwaters and urbanized lower reaches. Our study area was an impaired coldwater stream in Michigan, USA

Objectives

Methods

Results

Discussion

Conclusion