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</div> </td><td valign="top" width="24"></td><td valign="top"> <div align="left"> <table border="0" cellpadding="2" cellspacing="4" width="400" align="left"> <tr> <td width="336"></td> </tr> <tr> <td width="336"> <p><font color="#000000" face="Arial" size="6"><b> Assigning Load <br> and Waste Load Allocations</b></font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> This section deals especially with the allocation of loads to various polluters – perhaps the most </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> scientifically and politically challenging aspect of TMDLs. Setting and policing TMDLs requires </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> an understanding of the difference between concentration and load, so we will first examine that </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> key pair of values. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> The first step in writing a TMDL is determining the maximum allowable load: the amount of a </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> pollutant that the water body can tolerate without degradation. Then background loads (BLs), </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> waste load allocations (WLAs), load allocations (LAs), and margins of safety (MOSs) must be </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> allocated as fairly as possible. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> This is the place where time invested in stakeholder development really pays off! Stakeholders </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> should be involved through all stages of the process to assure that they accept, as much as pos-sible, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> the nature of the problems and the potential solutions. With the support of the stakeholders, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> a TMDL process can yield excellent results. On the other hand, without stakeholder involvement </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> and buy-in, writing and enforcing a TMDL can be a frustrating, fractious undertaking. </font></p> <p><font face="Times New Roman" SIZE="5" COLOR="#000000"> Concentrations vs. Loads </font></p> <p><font face="Times New Roman"><font SIZE="3" COLOR="#000000"> The TMDL program is oriented toward controlling </font><b><font FACE="CGFAAZ+Futura-Condensed" SIZE="3" COLOR="#000000">loads </font></b><font SIZE="3" COLOR="#000000">– measured in mass/time increments </font></font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">such as pounds per day – so it works especially well for concentrated point sources. The quality </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">of the water itself – the way it directly affects organisms, including humans – depends on the </font></p> <b> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> concentration </font></b><font face="Arial" SIZE="3" COLOR="#000000">of pollutants, which is measured in mass/volume units, such as mg/L. Though the </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">law regulates in terms of load (e.g., 56 pounds of phosphorus/day), assessing nonpoint sources </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">and monitoring in-stream water quality are typically handled by concentration (0.07 mg/L total </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">P). </font></p> <p><font face="Times New Roman"><font SIZE="3" COLOR="#000000">The connecting factor is </font><b><font FACE="CGFAAZ+Futura-Condensed" SIZE="3" COLOR="#000000">flow</font></b><font SIZE="3" COLOR="#000000">, which is not directly regulated in the TMDL process in most cases. </font></font></p> <p><font SIZE="3" COLOR="#000000" face="Times New Roman">As noted earlier, the relationship Load = Concentration x Flow defines the links among the three </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">variables. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">By assuming a given flow rate, the resultant concentration is determined by dividing the load by </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">the flow rate. For example, in the Tualatin River, midsummer flow rates average 150 cubic feet </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">per second (cfs), which corresponds to about 100 million gallons per day, or about 800 million </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">lbs. of water. 70-ppb total phosphorus (TP) is the maximum concentration at which beneficial </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">uses of the river are not impaired by excess algal growth. A concentration of 70 ppb TP at 150 </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">cfs flow corresponds to 56 lbs TP per day. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">A major tributary during this time may have flow rates of 10 cfs--at a target concentration of 50 </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">ppb TP for agricultural systems, this represents about 2.7 lb. of TP passing that point per day. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">Compared with simply collecting a water sample and analyzing concentrations, determining flow </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">rates in open channel systems is time-consuming. By monitoring flow at a minimum of ten </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">evenly spaced points across the stream, total flow can be determined. This may be done on every </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">visit to a site. Or, after these direct flow measurements have been taken over a wide range of </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">flow conditions, a relationship between depth at one point in the stream and the flow for the </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">whole stream can be developed. This relationship is called the "rating curve," and is generally </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">useful over the range of flows with which it was developed, as long as the channel shape doesn’t </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">change. Once a valid rating curve is available for a reach of stream, only one depth measurement </font></p> <p><font face="Times New Roman"><font SIZE="2" COLOR="#000000"> © </font><font SIZE="3" COLOR="#000000">1999, YSI Incorporated 40 </font></font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">needs to be taken to calculate flow. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">Controlling loads can be accomplished in one of two ways: lowering concentrations, or lowering </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">flow rates. For point sources, either approach is useful, because the flow is typically a small </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">fraction of the total input into the system. Excluding this small point source flow, basically all </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">the rest of the flow is from nonpoint sources. In contrast, eliminating nonpoint source load by </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">eliminating flow will dry up the stream or lake. So the best option is to maintain or even increase </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">flow, but focus on lowering concentrations in that water. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">Increasing flow can be achieved with stored water, timing reservoir releases to meet flow goals, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">establishing or restoring wetlands, and managing riparian buffers. In the Pacific Northwest, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">innovative water rights easements have been designed which allow water trusts to lease water </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">rights and direct them to instream use rather than irrigation (Landry and Peck, 1998). Instream </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">water rights could provide another valuable flow management tool, especially where the prior </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">appropriation doctrine of water law prevails. </font></p> <p><font face="Times New Roman" SIZE="4" COLOR="#000000"> Maximum Allowable Loads </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> Maximum allowable loads are determined based on the concentrations or amounts of pollutants </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> that will not degrade the quality of the </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> water body, adversely affecting its benefi-cial </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> uses. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> In many cases, research is required to </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> determine what these concentrations or </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> amounts are. A report is also available </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> which allows the user to determine specifi-cally </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> the types of algal or higher plant </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> species that are most likely to occur in a </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> given water body (NRCS/EPA, in press). </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> Based on the fundamental properties of the </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> stream or lake, the likely plant types or </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> responses can be predicted. In addition, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> this publication indicates the relative </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> sensitivity of water bodies to changes in </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> two important TMDL parameters, phospho-rus </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> and nitrogen. </font></p> <p><font face="Times New Roman" SIZE="4" COLOR="#000000"> Waste Load Allocations - Point Sources </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> Each major point source in a TMDL-affected watershed is allocated a quantity of additional </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> pollutant it can add to the water body – a waste load allocation, or WLA. In most instances these </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> systems are already regulated by the National Pollution Discharge Elimination System (NPDES </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> permits), which requires monitoring effluent flow rates and concentrations. Monitoring the </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> stream above and below a point source outfall is important for determining the actual impact of </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> the source on both the regulated parameter and other stream water quality parameters. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> It is important to note that waters coming from point sources differ from waters derived from </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> nonpoint sources in several ways: </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> 1. They often contain higher concentrations of pollutants </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> 2. Flow rates are relatively constant and predictable </font></p> <p><font face="Times New Roman" COLOR="#000000"> Experimentation Yields </font></p> <p><font face="Times New Roman" COLOR="#000000"> Maximum Allowable Load </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> To determine the critical concentration of total </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> phosphorus (TP) in Oregon’s Tualatin River, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> experiments were conducted with native algal </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> populations at different total P concentrations. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> It was found that there was some limitation to </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> algal growth below 70 micrograms TP/L. The </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> product of total flow and concentration gives </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> the total load of TP that the river can tolerate </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> without exceeding 70 micrograms TP/L, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> which results in excessive algal growth. </font></p> <p><font face="Times New Roman"><font SIZE="2" COLOR="#000000"> © </font><font SIZE="3" COLOR="#000000">1999, YSI Incorporated 41 </font></font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">3. The form of the pollutants is often different, with more soluble forms and less </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">particulate/sediment forms </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">4. Because it is concentrated in one point, and regulated by other programs (e.g., </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">NPDES, the National Pollution Discharge Elimination System), the loads are easily </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">calculated very accurately </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">As a result of these characteristics, in most cases, point sources cause the biggest problems </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">during dry season, low-flow periods, because the flow of the receiving water (the water the </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">point source empties into) is less and so there is less dilution of the concentrated point </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">source. </font></p> <p><font face="Times New Roman" SIZE="4" COLOR="#000000"> Load Allocations - Nonpoint Sources </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> A total load allocation (LA) is established to cover all nonpoint sources in a watershed </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> covered by a TMDL. This total LA is divided into individual allocations. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> The basis for this allocation rests on a wide range of factors, including estimates of sources, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> expected ability to meet the TMDL limits, and overall economics. There’s no question that </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> some cleanup strategies are cost-prohibitive. The TMDL process allows TMDL managers </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> and stakeholders to consider whether it is cheaper and more effective to clean up discharge </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> from one source, or to prevent further pollution from other sources. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> In many cases, a Designated Management Agency is chosen to represent each land use type – </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> such as a conservation district for agriculture, and a state department of forestry covering </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> woodlands – helping negotiate the level of allocation and institute best management prac-tices. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> Load allocation requires active participation of stakeholders in the watershed (see Section II). </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> For example, in the Tualatin River Valley, the allocation of phosphorus was roughly based on </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> expected concentrations coming out of stream reaches dominated by those land management </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> types: forestry at 20 micrograms of total phosphorus (TP)/L, agriculture at 50 micrograms </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> TP/L, and urban at 70 micrograms/L. Therefore, the load allocations were equivalent to 20, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> 30, and 20 microgram TP/L changes in concentration for forestry, agriculture, and urban, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> respectively. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> There are some general statements that apply to most nonpoint sources: </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> 1. Nonpoint sources often contain low concentrations of pollutants, but still too high for </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> aquatic health. In some cases, however, nonpoint sources can have very high concen-trations </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> – for instance, large livestock feedlots. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> 2. Flow is often much higher during rainy periods than dry periods because of its connec-tion </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> to runoff. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> 3. Nonpoint sources have not been monitored as intensively as point sources and have not </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> been regulated nearly as much or as consistently as point sources in the past. Rela-tively </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> speaking, little baseline data are available. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> 4. Because of their erratic nature, capturing the storm events that lead to large nonpoint </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> source pollution inputs is difficult in most monitoring programs, especially those that </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> rely on grab sampling. </font></p> <p><font face="Times New Roman"><font SIZE="2" COLOR="#000000"> © </font><font SIZE="3" COLOR="#000000">1999, YSI Incorporated 42 </font></font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">5. There is great uncertainty in predicting the amount of pollution from nonpoint </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">sources because they are so dispersed and generally have low concentrations. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">Given the many unknowns, it’s no surprise that modeling sources, transport, and sinks of </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">nonpoint source pollutants – and assigning reasonable loads comparable to point sources – is </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">difficult. </font></p> <p><font face="Times New Roman" SIZE="4" COLOR="#000000"> Background </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> Every natural water body contains most of the parameters managed with TMDLs. Nutrients and </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> sediments, in particular, are always present, although in some aquatic systems their natural </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> concentrations are very low. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> Thus, setting the TMDL for a given body of water generally assumes that there is a difference </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> between the natural background and the TMDL for a given beneficial use. This difference is </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> caused by human-related inputs, which can be then assigned LAs and WLAs. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> In a few cases, where backgrounds are naturally high or the water body is particularly sensitive, </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> there may be little or no difference between background loading from natural sources and the </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> TMDL. Any increase above the background conditions results in significant degradation of water </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> quality. In those cases, there is no flexibility to allow for enrichment above the background, and </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> the LAs and WLAs must be zero. Monitoring must be done to assure that there are no increases </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> above the background. </font></p> <p><font face="Times New Roman" SIZE="4" COLOR="#000000"> Margin of Safety </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> This is "insurance" based upon the certainty of the response of the system to the parameter in </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> question. As noted above, this depends on how well the water body is understood. If best </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> available science suggests that a given concentration of a nutrient will be low enough to limit </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> algal growth to acceptable levels, the MOS may dictate that the TMDL be set at 70% of that </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> concentration as a target, because of the uncertainty in that number. For example, as concentra-tions </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> decrease, other algal species may become dominant that require less nutrient for maximum </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> growth. So setting a margin of safety makes sense where the response of the water body is </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> uncertain. </font></p> <p><font face="Times New Roman" SIZE="5" COLOR="#000000"> TMDLs and Lakes </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> The TMDL approach is well suited to regulation of pollutants entering lakes. Of course, because </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> of long residence times, flow is less important than the amount of a pollutant that enters the </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> system. Most lakes have residence times of months to years, meaning that any pollutant entering </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> the system can remain in the system for a long time before it is flushed out, which can cause </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> many long-term problems. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> Any streams, pipes, or groundwater flows that enter the lake and bring pollutants can continue to </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> degrade lake health over the long term. Also, in contrast to flowing water systems, fine, nutrient-rich </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> sediments are likely to settle and accumulate in polluted lakes. In many cases these sedi-ments </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> become important long-term, internal sources of pollutants, which are difficult to eliminate </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> and keep cycling phosphorus into the water year after year. Such fine sediments rarely settle to </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> the bottom in streams, unless the streams are stagnant during part of the year. It’s important to </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000"> note that phosphorus – and, to a lesser extent, nitrogen – are often associated with sediments and </font></p> <p><font face="Times New Roman"><font SIZE="2" COLOR="#000000"> © </font><font SIZE="3" COLOR="#000000">1999, YSI Incorporated 43 </font></font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">accumulated organic matter in lakes. </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">As with TMDLs written for streams, TMDLs for lakes assign a load to the lake, then assign </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">portions of that load to the contributing sources of pollution: point sources, tributaries, groundwa-ter </font></p> <p><font face="Times New Roman" SIZE="3" COLOR="#000000">and sediments. </font></p> <p><font face="Times New Roman"><font SIZE="2" COLOR="#000000"> © </font><font SIZE="3" COLOR="#000000">1999, YSI Incorporated </font></font></p> </td> </tr> </table> </div> </td></tr></table></body> </html>