Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER), James Cook University, 1 James Cook Drive, Townsville 4811, Australia; Faculty of Science and Engineering, Southern Cross University, 1 Military Drive, Lismore 2480, Australia.
School of Natural Sciences, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand.
Water Res. 2023 Nov 1;246:120731. doi: 10.1016/j.watres.2023.120731. Epub 2023 Oct 12.
Nutrient enrichment is one of the most pervasive impacts on aquatic ecosystems globally. Approaches to establish nutrient criteria that safeguard aquatic ecosystem health are highly variable and, in many instances, criteria are derived from correlations between in-situ nutrient concentrations and biological indices. Summarising entire assemblages with a single index can result in a substantial loss of information and potentially weaker relationships. In this study, we compared the derivation of nutrient criteria using biological indices and those from individual taxa for rivers and streams in New Zealand. Random forest models, including nutrient concentrations, were built to predict two biological indices and individual taxa across New Zealand's river monitoring network. For all acceptable models, the response of the biological indices and individual taxa to increasing Dissolved Inorganic Nitrogen (DIN) and Dissolved Reactive Phosphorus (DRP) were then predicted for every river reach across the nation, and nutrient concentrations that protected 80% of taxa were then identified. Models for the biological indices were poor but were good for most of the taxa, with nutrient concentrations almost always being the most influential factor. To ensure persistence of at least 80% of the taxa within a river reach, we estimated that DIN (Dissolved Inorganic Nitrogen) concentrations would need to be below 0.57-1.32 mg/L, and DRP (Dissolved Reactive Phosphorus) concentrations below 0.019-0.033 mg/L, depending on the river type. In general, high order, low slope rivers and streams required more stringent nutrient criteria than steep, low order streams. The link between nutrient concentrations and biological indices were weak and likely suffer from the loss of information from summarising an entire assemblage into a single numeric. We consider that the derivation of nutrient criteria for waterways should also examine the individual relationships with the taxa in a river system to establish protection for a desired proportion of taxa.
营养富集是全球水生生态系统最普遍的影响之一。建立保护水生生态系统健康的营养标准的方法差异很大，在许多情况下，这些标准是根据原位营养浓度与生物指标之间的相关性得出的。用单一指标概括整个生物群落可能会导致大量信息丢失，并可能导致关系减弱。在这项研究中，我们比较了使用生物指标和个别分类单元来确定新西兰河流和溪流营养标准的方法。随机森林模型包括营养浓度，用于构建预测新西兰河流监测网络中两个生物指标和个别分类单元的模型。对于所有可接受的模型，然后预测生物指数和个别分类单元对溶解无机氮 (DIN) 和溶解反应磷 (DRP) 增加的响应，然后确定保护 80%分类单元的营养浓度。生物指数的模型很差，但对大多数分类单元都很好，营养浓度几乎总是最具影响力的因素。为了确保河流段内至少 80%的分类单元持续存在，我们估计 DIN（溶解无机氮）浓度需要低于 0.57-1.32 mg/L，DRP（溶解反应磷）浓度需要低于 0.019-0.033 mg/L，具体取决于河流类型。一般来说，高等级、低坡度的河流和溪流比陡峭、低等级的溪流需要更严格的营养标准。营养浓度与生物指标之间的联系较弱，并且可能因将整个生物群落概括为单个数字而导致信息丢失。我们认为，应通过检查河流系统中与分类单元的个别关系，为所需比例的分类单元建立保护，来制定水道的营养标准。
