The importance of nutrient supply by fish excretion and watershed streams to a eutrophic lake varies with temporal scale over 19 years
The importance of nutrient supply by fish excretion and watershed streams to a eutrophic lake varies with temporal scale over 19 years
复制标题
鱼类排泄物和分水岭溪流对富营养化湖泊的养分供应的重要性在 19 年来随时间尺度的变化而变化
作者：
T. Williamson;M. Vanni;María González;W. Renwick;M. T. Bremigan;J. Conroy
动物以生态相关的速率转化和转移营养物质，通过调动原本无法获得的营养物质，导致水生生态系统的富营养化。然而，我们对动物介导的营养循环与长期（数年至数十年）和多个时间尺度的外部非生物营养源的比较知之甚少。为了解决这个问题，我们在一个富营养化水库中进行了一项为期 19 年的研究，在每周、每月和季节性时间尺度上检查流域溪流的氮 (N) 和磷 (P) 输入与丰富鱼类（砂鲥鱼、Dorosoma cepedianum）的排泄量。在整个时间段内，流域的 N 和 P 负荷分别比鱼类 N 和 P 排泄量高 33 倍和 3 倍。然而，在生长季节，鱼类 N 排泄量在 36% 的周和 43% 的月份中超过了流域养分负荷，而鱼类 P 的排泄量在生长季节的 68% 的周和 58% 的月份中超过了流域养分负荷。与流域负荷相比，鱼类排泄在供应率和氮磷比方面的时间变异性较低。鱼类排泄物提供的营养物质 N:P 摩尔比也比流域低得多（每日 N:P 供应比平均值分别为 15 和 723）。在鱼类生物量高的富营养化湖泊中，鱼类排泄物会强烈影响藻类生物量和群落组成。除了其他流域管理措施以改善水质外，富营养化管理工作还应考虑去除底食性鱼类，例如砂鲥鱼。未来的气候变化将通过改变食性鱼类的地理分布以及风暴和干旱事件的频率和严重程度来调节鱼类和流域介导的营养动态之间的相互作用。
Animals transform and translocate nutrients at ecologically relevant rates, contributing to eutrophication in aquatic ecosystems by mobilizing otherwise unavailable nutrients. Yet we know little about how animal-mediated nutrient cycling compares with external abiotic nutrient sources over long periods (years–decades) and at multiple timescales. To address this, we conducted a 19-year study in a eutrophic reservoir examining nitrogen (N) and phosphorus (P) inputs from watershed streams versus excretion by an abundant fish (gizzard shad, Dorosoma cepedianum) at weekly, monthly and seasonal timescales. Over the entire time period, watershed N and P loading was 33- and 3-fold greater than fish N and P excretion, respectively. However, fish N excretion exceeded watershed nutrient loading in 36% of weeks and 43% of months, and fish P excretion in 68% of weeks and 58% of months during the growing season. Fish excretion had lower temporal variability in both supply rate and N:P ratio than watershed loading. Fish excretion also supplied nutrients at a much lower molar N:P ratio than the watershed (mean of daily N:P supply ratios were 15 and 723, respectively). In eutrophic lakes with high fish biomass, fish excretion can strongly influence algal biomass and community composition. Eutrophication management efforts should consider removal of benthivorous fish, like gizzard shad, in addition to other watershed management practices to improve water quality. Future climate change will modulate the interplay between fish- and watershed-mediated nutrient dynamics by altering the geographic distribution of detritivorous fish and the frequency and severity of storm and drought events.