National Marine Science Centre, School of Environment, Science and Engineering, Southern Cross University, Coffs Harbour, NSW, Australia; School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, Australia.
National Marine Science Centre, School of Environment, Science and Engineering, Southern Cross University, Coffs Harbour, NSW, Australia.
Sci Total Environ. 2016 Oct 1;566-567:1440-1453. doi: 10.1016/j.scitotenv.2016.06.008. Epub 2016 Jun 17.
The role of groundwater in transporting nutrients to coastal aquatic systems has recently received considerable attention. However, the relative importance of fresh versus saline groundwater-derived nutrient inputs to estuaries and how these groundwater pathways may alter surface water N:P ratios remains poorly constrained. We performed detailed time series measurements of nutrients in a tidal estuary (Hat Head, NSW, Australia) and used radium to quantify the contribution of fresh and saline groundwater to total surface water estuarine exports under contrasting hydrological conditions (wet and dry season). Tidally integrated nutrient fluxes showed that the estuary was a source of nutrients to the coastal waters. Dissolved inorganic nitrogen (DIN) export was 7-fold higher than the average global areal flux rate for rivers likely due to the small catchment size, surrounding wetlands and high groundwater inputs. Fresh groundwater discharge was dominant in the wet season accounting for up to 45% of total dissolved nitrogen (TDN) and 48% of total dissolved phosphorus (TDP) estuarine exports. In the dry season, fresh and saline groundwater accounted for 21 and 33% of TDN export, respectively. The combined fresh and saline groundwater fluxes of NO3, PO4, NH4, DON, DOP, TDN and TDP were estimated to account for 66, 58, 55, 31, 21, 53 and 47% of surface water exports, respectively. Groundwater-derived nitrogen inputs to the estuary were responsible for a change in the surface water N:P ratio from typical N-limiting conditions to P-limiting as predicted by previous studies. This shows the importance of both fresh and saline groundwater as a source of nutrients for coastal productivity and nutrient budgets of coastal waters.
地下水在向沿海水生系统输送养分方面的作用最近受到了相当多的关注。然而，新鲜地下水和咸地下水对河口的养分输入的相对重要性，以及这些地下水途径如何改变地表水的 N:P 比值，仍然受到很大的限制。我们对一个潮汐河口（澳大利亚新南威尔士州的 Hat Head）进行了详细的时间序列养分测量，并使用镭来量化在不同水文条件下（湿季和干季）新鲜水和咸地下水对总地表水河口出口的贡献。潮汐积分养分通量表明，河口是向沿海水域输送养分的源。溶解无机氮（DIN）的输出是全球平均面积河流通量的 7 倍，这可能是由于流域面积小、周围湿地和地下水输入高。在湿季，新鲜地下水排放占总溶解氮（TDN）和总溶解磷（TDP）河口出口的 45%。在干季，新鲜和咸地下水分别占 TDN 出口的 21%和 33%。估计新鲜和咸地下水的 NO3、PO4、NH4、DON、DOP、TDN 和 TDP 通量分别占地表水出口的 66%、58%、55%、31%、21%、53%和 47%。地下水向河口输入的氮是导致地表水 N:P 比值从典型的 N 限制条件转变为 P 限制条件的原因，这与之前的研究预测一致。这表明，新鲜水和咸地下水都是沿海生产力和沿海水域养分预算的重要养分来源。
