Gorman Daniel, Russell Bayden D, Connell Sean D
Southern Seas Ecology Laboratories, DP650 418, School of Earth and Environmental Sciences, University of Adelaide, South Australia 5005, Australia.
Ecol Appl. 2009 Jul;19(5):1114-26. doi: 10.1890/08-0831.1.
Spatial subsidies are considered strong where differences in resource availability between donor and recipient systems are greatest. We tested whether human activities on land can increase subsidies of terrigenous nitrogen to open rocky coasts and whether these differences can predict apparent deforestation of kelp forests. We first identified landscape-scale variation in the human-mediated transfer of dissolved inorganic nitrogen (DIN) from natural, agricultural, and urban catchments to temperate coasts after episodes of rainfall. Compared to natural catchments, subsidies of DIN were on average 8-407 times greater in urban catchments, and 1-63 times greater in agricultural catchments. Urban derived nitrogen was attributed to the release of sewage effluent, as delineated by delta15N isotopic values of transplanted algae. Having made this link, we then assessed whether this catchment-scale variation may account for variation in structure of subtidal habitats, particularly as related to theory of nutrient-driven shifts of habitat from perennial (i.e., canopy-forming algae) to opportunistic species (i.e., turf-forming algae). We not only detected patterns consistent with this theory, but also established that the size and total proportion of patches of turf-forming algae were greater where the ratio of donor: recipient nitrogen loads was greater (i.e., size of subsidy). An important realization was that deforestation may be more strongly related to variation in the size of subsidy rather than size of human populations, particularly among urban catchments. These data directly link the type of human activity within catchments to the modification of land-to-sea subsidies and indirectly support theory that predicts terrestrial inputs to have greater ecological effects where the disparity in resource availability between donor and recipient is exacerbated. Our evidence has been used by coastal managers to reconsider their management of coastal systems and has subsequently contributed to new water-recycling policy and initiatives.
当供体系统和受体系统之间资源可利用性的差异最大时，空间补贴被认为是强大的。我们测试了陆地上的人类活动是否会增加陆源氮向开阔岩石海岸的补贴，以及这些差异是否可以预测海带森林明显的砍伐情况。我们首先确定了降雨事件后，人类介导的溶解无机氮（DIN）从自然、农业和城市集水区向温带海岸转移的景观尺度变化。与自然集水区相比，城市集水区DIN的补贴平均高出8 - 407倍，农业集水区高出1 - 63倍。城市来源的氮归因于污水排放，这是通过移植藻类的δ15N同位素值来确定的。建立这种联系后，我们接着评估这种集水区尺度的变化是否可以解释潮下带栖息地结构的变化，特别是与营养驱动的栖息地从多年生（即形成冠层的藻类）向机会主义物种（即形成草皮的藻类）转变的理论相关。我们不仅检测到了与该理论一致的模式，还确定了在供体：受体氮负荷比更大（即补贴规模）的地方，形成草皮的藻类斑块的大小和总比例更大。一个重要的认识是，森林砍伐可能与补贴规模的变化比与人口规模的变化更密切相关，特别是在城市集水区中。这些数据直接将集水区内人类活动的类型与陆地到海洋补贴的改变联系起来，并间接支持了一种理论，即预测在供体和受体之间资源可利用性差异加剧的地方，陆地输入具有更大的生态影响。我们的证据已被沿海管理者用于重新考虑他们对沿海系统的管理，并随后促成了新的水循环政策和举措。
