Seasonal patterns in streamwater nutrient and dissolved organic carbon concentrations: Separating catchment flow path and in‐stream effects
Seasonal patterns in streamwater nutrient and dissolved organic carbon concentrations: Separating catchment flow path and in‐stream effects
复制标题
溪流营养物和溶解有机碳浓度的季节性模式：分离流域流动路径和河内效应
DOI：
10.1029/97wr00490
复制
发表时间：
1997
影响因子：
5.4
通讯作者：
W. Hill
中科院分区：
文献类型：
--
作者：
P. Mulholland;W. Hill
在步行者分支（WB）的西叉7年每周采样的数据记录和附近的流，上白色橡树溪（WOC），在田纳西州东部的岭谷省的一级流每周采样4年的数据记录中，明显的溪流营养盐和溶解有机碳（DOC）浓度的季节性模式。NO3和可溶性活性磷（SRP）在两个流的浓度表现出重复的模式，一年最大值在夏季和两年最小值在秋季和春季。WB中DOC浓度呈现明显的秋季最大值。为了确定流域水文过程的时间变化是否可以解释WB中的季节性营养盐和DOC变化，我们使用了涉及Ca和SO4浓度的端元混合分析，将河流排放分为三个不同营养盐浓度的流域流动路径。流NO3，SRP和DOC浓度的预测仅在时间变化的基础上的重要性，这些流动路径和测量的营养物质浓度的不同流动路径。溪流中观测/预测浓度的比值接近1.0，表明集水效应单独解释了溪流浓度，而比值与1.0的差异很大，表明溪流中的过程是溪流浓度的重要决定因素。观测/预测的NO3和SRP浓度比显示出重复的年度模式，冬季和夏季的值接近1.0（通常为0.8 - 1.2），春季和秋季的最小值（<0.6），表明这些时间的大量流净吸收。观测/预测的DOC浓度比变化更大，通常≥ 1，但确实显示出一致的秋季最大值（> 2.5），表明此时大量的流内DOC生成。所有营养物的观测/预测比值通常变化较小，与低流量相比，在高流量下更接近1.0，这表明在高流量下对河水化学的流内控制不如低流量下重要。我们的研究结果表明，河流营养盐浓度的控制有两种一般模式：（1）通过主要水文途径的季节变化（夏季深层地下水的比例较大）进行集水控制，冬季浓度较低，夏季浓度较高;（2）通过春季（主要由自养生物）和秋季（主要由异养生物）的高净营养吸收率进行流内控制。
Distinct seasonal patterns in streamwater nutrient and dissolved organic carbon (DOC) concentrations are evident in the data record from 7 years of weekly sampling in the West Fork of Walker Branch (WB) and 4 years of weekly sampling in a nearby stream, upper White Oak Creek (WOC), both first‐order streams in the Ridge and Valley Province of eastern Tennessee. Concentrations of NO3 and soluble reactive phosphorus (SRP) in both streams showed a repeated pattern of annual maxima in summer and biannual minima in autumn and spring. Concentrations of DOC in WB exhibited distinct autumn maxima. To determine whether temporal variations in catchment hydrological processes could explain the seasonal nutrient and DOC variations in WB, we used an end‐member mixing analysis involving Ca and SO4 concentrations to separate stream discharge into three catchment flow paths of differing nutrient concentrations. Stream NO3, SRP, and DOC concentrations were predicted solely on the basis of temporal variation in the importance of these flow paths and measurements of nutrient concentrations for the different flow paths. Ratios of observed/predicted concentrations in stream water near 1.0 suggested that catchment effects alone explained streamwater concentrations, whereas ratios substantially different from 1.0 suggested that in‐stream processes were important determinants of streamwater concentrations. Observed/predicted NO3 and SRP concentration ratios showed repeated annual patterns with values closer to 1.0 during winter and summer (generally 0.8–1.2) and minima (<0.6) in spring and autumn, suggesting substantial in‐stream net uptake at these times. Observed/predicted DOC concentration ratios were more variable and generally ≥1 but did show consistent autumn maxima (>2.5), indicating substantial in‐stream DOC generation at this time. Observed/predicted ratios for all nutrients were generally less variable and were closer to 1.0 at high flow compared to low flow, suggesting that in‐stream controls on streamwater chemistry are less important at high discharge than at low discharge. Our results indicate two general modes of control of stream nutrient concentrations: (1) catchment control via seasonal variation in the dominant hydrologic pathway (greater proportion of deep groundwater in summer), which produces lower winter and higher summer concentrations, and (2) in‐stream control via high rates of net nutrient uptake during the spring (primarily by autotrophs) and autumn (primarily by heterotrophs).