River water quality changes in New Zealand over 26 years: response to land use intensity
River water quality changes in New Zealand over 26 years: response to land use intensity
复制标题
DOI：
10.5194/hess-21-1149-2017
复制
发表时间：
2017-02-23
影响因子：
6.3
通讯作者：
Ausseil, Anne-Gaelle E.
中科院分区：
文献类型：
--
作者：
Julian, Jason P.;de Beurs, Kirsten M.;Ausseil, Anne-Gaelle E.
土地利用和水质之间的关系是复杂的，具有相互依存、反馈和遗留影响。大多数河流水质研究都以面积覆盖率来评估集水区土地利用，但在这里，我们假设并检验土地利用强度-土地利用的投入(化肥、牲畜)和活动(植被清除)是否能更好地预测环境影响。我们使用新西兰(新西兰)作为案例研究，因为近几十年来，新西兰是全球农业用地集约化率最高的国家之一。我们在国家河流水质网络(NRWQN)中解释了从1989年到2014年的26年间的水质状况和趋势。NRWQN由35个主要是大型河流系统的77个站点组成。为了表征土地利用强度，我们分析了集水区尺度上牲畜密度和土地干扰(即放牧或森林采伐造成的植被丧失造成的裸露土壤)的时空变化，以及国家尺度上的化肥投入。使用对77个集水区的简单多变量统计分析，我们发现，集约化管理的牧场的面积覆盖对中位数视觉水清晰度的预测效果最好。然而，对所有四个营养变量(TN、NOx、TP、DRP)的主要预测因子是牛密度，人工林覆盖率是次要预测变量。虽然土地干扰本身并不是水质的有力预测指标，但它确实有助于解释土地利用-水质关系的离群值。从1990年到2014年，77个集水区中的35个(34=77个)的视觉清晰度显著提高，我们主要归因于更多的奶牛被排除在河流之外(尽管奶牛数量增加)，以及整个新西兰的绵羊数量大幅减少，从1990年的5800万只羊减少到2012年的3100万只羊。新西兰许多河流的营养物质浓度增加，27/77流域的溶解氧化氮显著增加，我们在很大程度上归因于牛密度的增加和自20世纪50年代以来在集约化管理的草原和人工林中积累起来的遗留营养物质，并正在慢慢泄漏到河流中。尽管新西兰一些河流的水质最近有所改善，但这些遗留的营养物质和持续的农业集约化预计将在未来几十年造成广泛的环境问题。
Relationships between land use and water quality are complex with interdependencies, feedbacks, and legacy effects. Most river water quality studies have assessed catchment land use as areal coverage, but here, we hypothesize and test whether land use intensity - the inputs (fertilizer, livestock) and activities (vegetation removal) of land use is a better predictor of environmental impact. We use New Zealand (NZ) as a case study because it has had one of the highest rates of agricultural land intensification globally over recent decades. We interpreted water quality state and trends for the 26 years from 1989 to 2014 in the National Rivers Water Quality Network (NRWQN) - consisting of 77 sites on 35 mostly large river systems. To characterize land use intensity, we analyzed spatial and temporal changes in livestock density and land disturbance (i.e., bare soil resulting from vegetation loss by either grazing or forest harvesting) at the catchment scale, as well as fertilizer inputs at the national scale. Using simple multivariate statistical analyses across the 77 catchments, we found that median visual water clarity was best predicted inversely by areal coverage of intensively managed pastures. The primary predictor for all four nutrient variables (TN, NOx, TP, DRP), however, was cattle density, with plantation forest coverage as the secondary predictor variable. While land disturbance was not itself a strong predictor of water quality, it did help explain outliers of land use-water quality relationships. From 1990 to 2014, visual clarity significantly improved in 35 out of 77 (34 = 77) catchments, which we attribute mainly to increased dairy cattle exclusion from rivers (despite dairy expansion) and the considerable decrease in sheep numbers across the NZ landscape, from 58 million sheep in 1990 to 31 million in 2012. Nutrient concentrations increased in many of NZ's rivers with dissolved oxidized nitrogen significantly increasing in 27/77 catchments, which we largely attribute to increased cattle density and legacy nutrients that have built up on intensively managed grasslands and plantation forests since the 1950s and are slowly leaking to the rivers. Despite recent improvements in water quality for some NZ rivers, these legacy nutrients and continued agricultural intensification are expected to pose broad-scale environmental problems for decades to come.