Vanni Michael J, Bowling Anna M, Dickman Elizabeth M, Hale R Scott, Higgins Karen A, Horgan Martin J, Knoll Lesley B, Renwick William H, Stein Roy A
Department of Zoology, Miami University, Oxford, Ohio 45056, USA.
Ecology. 2006 Jul;87(7):1696-709. doi: 10.1890/0012-9658(2006)87[1696:ncbfsr]2.0.co;2.
Animals can be important in nutrient cycling in particular ecosystems, but few studies have examined how this importance varies along environmental gradients. In this study we quantified the nutrient cycling role of an abundant detritivorous fish species, the gizzard shad (Dorosoma cepedianum), in reservoir ecosystems along a gradient of ecosystem productivity. Gizzard shad feed mostly on sediment detritus and excrete sediment-derived nutrients into the water column, thereby mediating a cross-habitat translocation of nutrients to phytoplankton. We quantified nitrogen and phosphorus cycling (excretion) rates of gizzard shad, as well as nutrient demand by phytoplankton, in seven lakes over a four-year period (16 lake-years). The lakes span a gradient of watershed land use (the relative amounts of land used for agriculture vs. forest) and productivity. As the watersheds of these lakes became increasingly dominated by agricultural land, primary production rates, lake trophic state indicators (total phosphorus and chlorophyll concentrations), and nutrient flux through gizzard shad populations all increased. Nutrient cycling by gizzard shad supported a substantial proportion of primary production in these ecosystems, and this proportion increased as watershed agriculture (and ecosystem productivity) increased. In the four productive lakes with agricultural watersheds (>78% agricultural land), gizzard shad supported on average 51% of phytoplankton primary production (range 27-67%). In contrast, in the three relatively unproductive lakes in forested or mixed-land-use watersheds (>47% forest, <52% agricultural land), gizzard shad supported 18% of primary production (range 14-23%). Thus, along a gradient of forested to agricultural landscapes, both watershed nutrient inputs and nutrient translocation by gizzard shad increase, but our data indicate that the importance of nutrient translocation by gizzard shad increases more rapidly. Our results therefore support the hypothesis that watersheds and gizzard shad jointly regulate primary production in reservoir ecosystems.
动物在特定生态系统的养分循环中可能很重要，但很少有研究考察这种重要性如何随环境梯度而变化。在本研究中，我们量化了一种丰富的食碎屑鱼类——遮目鱼（Dorosoma cepedianum）在沿生态系统生产力梯度的水库生态系统中的养分循环作用。遮目鱼主要以沉积物碎屑为食，并将源自沉积物的养分排泄到水柱中，从而介导养分向浮游植物的跨生境转移。我们在四年期间（16个湖年）对七个湖泊中遮目鱼的氮和磷循环（排泄）速率以及浮游植物的养分需求进行了量化。这些湖泊跨越了流域土地利用（农业用地与森林用地的相对比例）和生产力的梯度。随着这些湖泊的流域越来越多地被农业用地主导，初级生产率、湖泊营养状态指标（总磷和叶绿素浓度）以及通过遮目鱼种群的养分通量均有所增加。遮目鱼的养分循环支持了这些生态系统中相当一部分的初级生产，并且这一比例随着流域农业（和生态系统生产力）的增加而增加。在四个具有农业流域（农业用地>78%）的富营养湖泊中，遮目鱼平均支持了51%的浮游植物初级生产（范围为27 - 67%）。相比之下，在三个位于森林或混合土地利用流域（森林>47%，农业用地<52%）的相对贫营养湖泊中，遮目鱼支持了18%的初级生产（范围为14 - 23%）。因此，沿着从森林景观到农业景观的梯度，流域养分输入和遮目鱼的养分转移都增加了，但我们的数据表明，遮目鱼养分转移的重要性增加得更快。因此，我们的结果支持了流域和遮目鱼共同调节水库生态系统初级生产的假设。
