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 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. Many 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. Environmental 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.

中文翻译：

---

将环境变量与农业/城市冷水流中的水生群落结构相关联

城市地区通常建在大河沿岸，周围环绕着农田。这可能会导致形成具有农业源头和城市化下游的小型支流。我们评估的研究目标如下：(1) 景观、地貌和水质变量，最能解释水生群落的变化及其在遵循这种农业到城市土地利用梯度的河流系统中的完整性；(2) 这种土地利用梯度导致水生群落与理想化的自然河流或其他纵向梯度的预期不同的方式；(3) 这种土地利用梯度对水生群落的影响是否会通过农业和城市发展在下游方向上变得更大。我们的研究区域是美国密歇根州一条受损的冷水流。许多因素构成了沿农业到城市土地利用梯度的生物群落。河内木质碎屑与 EPT（蜉蝣目、鳞翅目和毛翅目）丰度和丰富度的关系最强，并且在较低的城市化流域中最为常见。细河床基质与双翅目类群和地表空气呼吸型大型无脊椎动物的关系最强，在农业源头中占主导地位。鱼类群落组合在很大程度上受河流流量和温度状况的影响，而城市下游地区较差的鱼类群落完整性可能受到地貌和偶发性城市污染事件的影响。大型无脊椎动物在森林砍伐的一级农业源头中最为丰富，而 EPT 大型无脊椎动物的丰度是市区内农业区下游最高的，拥有广泛的森林缓冲区。环境变量和水生群落通常不符合我们对理想化自然溪流的期望。农业区下游的 EPT 丰富度有所提高。这显示了在具有这种从农业到城市的土地利用模式的流域中使用精心规划的管理来恢复水生系统的希望。小块森林可能是保护城市化景观中水生生物多样性的关键。这些发现对于研究遵循这种常见的农业到城市土地利用梯度的河流系统的研究人员和水资源管理人员的国际受众很有价值，