Total Maximum Daily Load (TMDL) - Lakes 2018

The Clean Water Act Section 303(d) establishes the Total Maximum Daily Load (TMDL) program. The purpose of the TMDL program is to identify sources of pollution and allocate pollutant loads in places where water quality goals are not being achieved. This layer shows the list of waters for which technology-based or other required pollution controls are not stringent enough to meet water quality standards. The TMDLs themselves specify a pollutant budget that must be achieved to meet state water quality standards and allocates pollutant loads among pollution sources in a watershed, e.g., point and nonpoint sources.
This layer represents lakes with TMDL associated with them. Lakes have characteristics that differentiate TMDLs from other waters. Lakes are not free-flowing like streams, but are contained waters that trap pollutants for long periods. Most lake impairments are from high nutrient or sediment loads. Wherever possible, lake TMDLs are developed with the information in the lake study reports that were sponsored by local watershed groups or other local interests. Target acceptable pollutant loads are set at the level of a watershed largely unaffected by human induced impacts. Load allocations are given to the pollutant sources using the same methods as nonpoint source TMDLs. Other indicators of water quality are also considered in the evaluation of a lake. One indicator is the Trophic Status Index (TSI), which refers to the degree of nutrient enrichment in the lake. Nutrient enrichment causes growths of algae that consume oxygen and interfere with the health of the aquatic organisms in the lake. The TSI is affected by factors such as lake volume, water residence time and nutrient loads to the lake. After target loads are set, the TSI is evaluated under reduced nutrient load conditions to assure that the pollutant reductions will bring the TSI into an acceptable range. Implementation of lake TMDLs is best accomplished though local participation. This layer is based on the High Resolution National Hydrography Dataset (NHD).

This data is hosted at, and may be downloaded or accessed from PASDA, the Pennsylvania Spatial Data Access Geospatial Data Clearinghouse http://www.pasda.psu.edu/uci/DataSummary.aspx?dataset=1131

《清洁水法案》第三百零三条（d）款确立了总最大日负荷（TMDL）计划。TMDL计划旨在识别污染源并分配未达成水质目标地区的污染物负荷。该图层展示了那些基于技术或其他必需的污染控制措施不足以满足水质标准的河流清单。TMDL本身规定了必须实现的污染物预算，以符合州水质标准，并在流域内将污染物负荷分配给污染源，例如，点源和非点源。本图层代表与TMDL相关的湖泊。湖泊具有将TMDL与其他水体区分开来的特征。湖泊并非如溪流般自由流动，而是蓄积水体，能够长时间捕捉污染物。大多数湖泊的退化源于高营养物或沉积物负荷。在可能的情况下，湖泊TMDL将与由地方流域团体或其他地方利益相关者资助的湖泊研究报告中的信息共同制定。目标可接受的污染物负荷被设定在受人类诱导影响较小的大流域水平。采用与非点源TMDL相同的分配方法，将负荷分配给污染物源。在评估湖泊水质时，也会考虑其他水质指标。一个指标是营养状态指数（TSI），它指的是湖泊中营养富集的程度。营养富集会导致藻类生长，消耗氧气并干扰湖泊中水生生物的健康。TSI受湖泊体积、水停留时间和湖泊的营养负荷等因素的影响。在设定目标负荷后，TSI将在减少营养负荷的条件下进行评估，以确保污染物减少将TSI纳入可接受的范围内。湖泊TMDL的实施最好通过地方参与来完成。本图层基于高分辨率国家水文数据集（NHD）。此数据由PASDA（宾夕法尼亚空间数据访问地理空间数据交换中心）托管，可从http://www.pasda.psu.edu/uci/DataSummary.aspx?dataset=1131下载或访问。