Assessing Ecosystem Structure and Function in an Urban Canal and Logan River, Utah

Humans have been creating artificial aquatic ecosystems for thousands of years. Some of these aquatic ecosystems are highly managed, especially in the semi-arid, Intermountain West. Here, humans have constructed extensive conveyance systems to support agriculture, to mitigate flooding, and to discharge stormwater. Despite their regional prevalence, the ecological structure and functioning of these conveyance systems remains largely unknown. To address this gap, I addressed the following questions: 1) How do water quality, freshwater invertebrate assemblages, and leaf decomposition compare between the Northwest Field Canal and its water source, an urbanized reach of the Logan River? 2) How do these measures change longitudinally in both waterways as they traverse Logan City? and 3) Which of the physical, chemical, and biological factors I measured most strongly influence leaf decomposition in these waterways? I collected water quality and freshwater invertebrate samples, and I measured leaf decomposition at twenty sites along the Logan River and an urban canal. I used Spearman’s correlation coefficients to evaluate the associations between physical, chemical, and biological factors and leaf decomposition. Water quality was similar between waterways, except for the most downstream site of the Logan River, which had elevated concentrations of nutrients and metals, and lower richness and abundance of invertebrates. Leaf decomposition occurred faster in the canal, and the canal had higher biomass of shredders compared to the Logan River. Facultative shredders were associated with the decay rate in the canal, suggesting that these shredders are associated with leaf decomposition. Leaf decomposition was faster at downstream sites in both waterways relative to the upstream sites, due to an abundance of facultative shredders in the canal and elevated nutrients at the most downstream site in the Logan River. Water velocity was associated with leaf decomposition in both waterways, and total phosphorus was positively associated with biomass of shredders and leaf decomposition, the latter of which is likely due to enhanced microbial activity.

数千年来，人类一直致力于构建人工水生生态系统。其中部分生态系统采用了高度管控的管理模式，在半干旱的山间西部（Intermountain West）尤为如此。在此区域，人类修建了大规模的输水系统（conveyance system），用以支撑农业生产、缓解洪涝灾害并排放雨水径流。尽管这类输水系统在区域内分布广泛，但其生态结构与生态功能在很大程度上仍未被探明。为填补这一研究空白，本研究围绕以下三个问题展开：1）西北田间渠（Northwest Field Canal）与其水源——洛根河（Logan River）的城市化河段——在水质、淡水无脊椎动物群落（freshwater invertebrate assemblages）以及叶片分解（leaf decomposition）方面存在何种差异？2）这两条水系流经洛根市（Logan City）的过程中，上述各项指标沿河道纵向会发生怎样的变化？3）本研究测得的物理、化学与生物因子中，哪些对这两条水系内的叶片分解过程影响最为显著？本研究在洛根河与一条城市输水渠沿线共设置20个采样点，采集了水质与淡水无脊椎动物样本，并测定了叶片分解速率。本研究采用斯皮尔曼相关系数（Spearman's correlation coefficient），分析物理、化学与生物因子与叶片分解过程之间的关联。两条水系的整体水质较为相似，但洛根河最下游的采样点除外：该点位的营养盐与金属浓度均偏高，同时无脊椎动物的物种丰富度与个体丰度均较低。输水渠内的叶片分解速率更快，且渠内撕食者（shredder）的生物量显著高于洛根河。兼性撕食者与输水渠内的叶片腐烂速率存在显著关联，这表明此类撕食者参与了叶片分解过程。相较于上游采样点，两条水系的下游采样点均表现出更快的叶片分解速率：这一现象的成因分别是输水渠内兼性撕食者的大量富集，以及洛根河最下游点位的营养盐浓度升高。两条水系内的水流速度均与叶片分解过程存在关联；总磷浓度则与撕食者生物量及叶片分解速率均呈正相关，后者可能是因为总磷提升了微生物的活性。