Calculating optical water quality targets to restore and protect submersed aquatic vegetation: Overcoming problems in partitioning the diffuse attenuation coefficient for photosynthetically active radiation
Calculating optical water quality targets to restore and protect submersed aquatic vegetation: Overcoming problems in partitioning the diffuse attenuation coefficient for photosynthetically active radiation
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DOI：
10.2307/1353240
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发表时间：
2001-06-01
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影响因子：
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通讯作者：
Gallegos, CL
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作者：
Gallegos, CL
沉水水生植被(SAV)是近几十年来急剧衰退的浅水河口系统的重要组成部分。SAV对光的要求特别高，在许多情况下，SAV的损失被归因于水柱中光衰减的增加，通常是由于沿海富营养化。为了将这些宝贵的栖息地恢复到其历史水平，需要一种简单但准确的管理工具，将光需求转化为能够支持SAV社区的水质目标。通过将光合作用有效辐射的扩散衰减系数Kd(PAR)表示为水加上有色溶解有机物(CDOM)、叶绿素和TSS的贡献的线性函数，推导了计算叶绿素和总悬浮固体(TSS)浓度的水质目标的方法。假定Kd(PAR)符合朗伯-比尔定律。目标浓度被确定为一条表示通过管理行动有意减少TSS和叶绿素的直线与另一条描述TSS对恒定Kd(PAR)的叶绿素的依赖关系的直线的交点。通过比较线性Kd(PAR)模型与更真实的光衰减模型模拟的数据，验证了Lambert-Beer定律应用于河口水域Kd(PAR)的有效性。线性回归模型在高光衰减时倾向于低估Kd(PAR)，导致对浅层恢复深度的目标浓度的错误预测。这些误差更多地是由PAR的宽光谱带宽造成的，而不是由漫反射衰减系数本身的不可恢复的非线性造成的。尽管Lambert-Beer定律不适用于Kd(PAR)，但由更具机械性的衰减模型确定的TSS与恒定Kj(PAR)下的叶绿素的变化是高度线性的。基于交叉线的管理工具的使用仍然是可能的，但是描述TSS对恒定Kd(PAR)的叶绿素的依赖的线中的系数必须通过应用为感兴趣区域适当校准的光学模型来经验地确定。对来自马里兰州罗德河的数据的实例应用表明，要将SAV的生长条件恢复到20世纪60年代末的水平，TSS和叶绿素浓度都需要减少约15%，或仅叶绿素减少50%。
Submersed aquatic vegetation (SAV) is an important component of shallow water estuarine systems that has declined drastically in recent decades. SAV has particularly high light requirements, and losses of SAV have, in many cases, been attributed to increased light attenuation in the water column, frequently due to coastal eutrophication. The desire to restore these valuable habitats to their historical levels has created the need for a simple but accurate management tool for translating light requirements into water quality targets capable of supporting SAV communities. A procedure for calculating water quality targets for concentrations of chlorophyll and total suspended solids (TSS) is derived, based on representing the diffuse attenuation coefficient for photosynthetically active radiation, Kd(PAR), as a linear function of contributions due to water plus colored dissolved organic matter (CDOM), chlorophyll, and TSS. It is assumed that Kd(PAR) conforms to the Lambert-Beer law. Target concentrations are determined as the intersection of a line representing intended reduction of TSS and chlorophyll by management actions, with another line describing the dependence of TSS on chlorophyll at a constant value of Kd(PAR). The validity of applying the Lambert-Beer law to Kd (PAR) in estuarine waters was tested by comparing the performance of a linear model of Kd(PAR) with data simulated using a more realistic model of light attenuation. The linear regression model tended to underestimate Kd(PAR) at high light attenuation, resulting in erroneous predictions of target concentrations at shallow restoration depths. The errors result more from the wide spectral bandwidth of PAR, than from irrecoverable nonlinearities in the diffuse attenuation coefficient per se. In spite of the failure of the Lambert-Beer law applied to Kd(PAR), the variation of TSS with chlorophyll at constant Kj(PAR) determined by the more mechanistic attenuation model was, nevertheless, highly linear. Use of the management tool based on intersecting lines is still possible, but coefficients in the line describing the dependence of TSS on chlorophyll at constant Kd(PAR) must be determined empirically by application of an optical model suitably calibrated for the region of interest. An example application of the procedure to data from the Rhode River, Maryland, indicates that approximately 15% reduction in both TSS and chlorophyll concentrations, or 50% reduction in chlorophyll alone, will be needed to restore conditions for growth of SAV to levels that existed in the late 1960s.