We developed a method to predict the susceptibility of New Zealand estuaries to eutrophication. This method predicts macroalgae and phytoplankton responses to potential nutrient concentrations and flushing times, obtained nationally from simple dilution models, a GIS land-use model and physical estuary properties. Macroalgal response was based on an empirically derived relationship between potential nitrogen concentrations and an established macroalgal index (EQR) and phytoplankton response using an analytical growth model. Intertidal area was used to determine which primary producer was likely to lead to eutrophic conditions within estuaries. We calculated the eutrophication susceptibility of 399 New Zealand estuaries and assigned them to susceptibility bands A (lowest expected impact) to D (highest expected impact). Twenty-seven percent of New Zealand estuaries have high or very high eutrophication susceptibilities (band C or D), mostly (63% of band C and D) due to macroalgae. The physical properties of estuaries strongly influence susceptibility to macroalgae or phytoplankton blooms, and estuaries with similar physical properties cluster spatially around New Zealand’s coasts. As a result, regional patterns in susceptibility are apparent due to a combination of estuary types and land use patterns. The few areas in New Zealand with consistently low estuary eutrophication susceptibilities are either undeveloped or have estuaries with short flushing times, low intertidal area and/or minimal tidal influx. Estuaries with conditions favourable for macroalgae are most at risk. Our approach provides estuary-integrated susceptibility scores likely to be of use as a regional or national screening tool to prioritise more in-depth estuary assessments, to evaluate likely responses to altered nutrient loading regimes and assist in developing management strategies for estuaries.

我们开发了一种方法来预测新西兰河口富营养化的易感性。该方法可预测大型藻类和浮游植物对潜在养分浓度和冲水时间的响应，该方法可从全国范围内的简单稀释模型，GIS土地利用模型和河口物理特性中获得。大型藻类反应基于潜在的氮浓度与已建立的大型藻类指数（EQR）和浮游植物反应之间的经验关系，该关系使用分析性生长模型。潮间带面积用于确定哪个主要生产者可能导致河口内发生富营养化状况。我们计算了399个新西兰河口的富营养化敏感性，并将它们分配给敏感性带A（预期影响最低）至D（预期影响最高）。百分之二十七的新西兰河口富营养化敏感性很高或很高（C或D带），大部分（C和D带的63％）归因于大型藻类。河口的物理特性强烈影响大型藻类或浮游植物水华的敏感性，并且具有相似物理特性的河口在空间上聚集在新西兰海岸附近。结果，由于河口类型和土地利用方式的结合，地区的易感性模式显而易见。新西兰很少有河口富营养化敏感性持续较低的地区，或者河口冲水时间短，潮间带面积小和/或潮汐涌入量少。条件有利于大型藻类的河口风险最大。