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<br /> will be most effective in reducing nutrient loading to the lake, it is important to recognize that this
<br /> watershed is not dominated by point source loading.
<br /> One source of nutrients, atmospheric Sources of Total Nitrogen Load Delivered to Falls Lake
<br /> deposition, affects all the land uses and 1.65 million pounds per year(2014 to 2018)
<br /> 7%from waateweter
<br /> waterbodies in the watershed including the ,reatmen,plen,a
<br /> Imajon minor,5500,
<br /> surface of Falls Lake, and not all of this 3%f-DOT. e.646
<br /> x%
<br /> 4z,72otram Dnaim
<br /> source originates within the watershed. While wa,ewaer
<br /> treetmen,systems.
<br /> atmospheric deposition of nitrogen has / 31,5at
<br /> decreased by approximately 20 percent since ryDePW e�=.
<br /> Lake Surfaces.
<br /> the baseline period based on monitoring data 96,961
<br /> from the National Atmospheric Deposition 1%`o on'r 12,925nk
<br /> AW
<br /> Pro ram it still contributes more than 1%from 19
<br /> , system mass,,1}9,752
<br /> 40 percent of the total nitrogen that is
<br /> applied or deposited to the watershed. Note
<br /> that not all of this load is delivered to the
<br /> lake. Figure 8 shows the projected amounts Sources of Total Phosphorus Load Delivered to Falls Lake
<br /> of nutrient load delivered from watershed 163,000 pounds per year(2014 to 20181
<br /> sources to Falls Lake. There is also a 1a%from
<br /> AgrlculTure,k8,657 11%from Urban,component of the load that falls directly onto 19,406
<br /> lake surfaces, and this contributes 1%from DOT,2.255
<br /> approximately 6 percent of the total nitrogenrI 4%from wa=t—Ter
<br /> treatment plants(major,
<br /> load to Falls Lake. As a point of reference, minnr,55oa,,6.465
<br /> this percentage of loading from the1%from onsite
<br /> w.atewater,teatrnent
<br /> atmosphere directly to the lake surface is the - sya,em=•1,125
<br /> same contribution of total nitrogen load 1%from Wet and Dry
<br /> 1.delivered from point sources. Depnaitinn 2,2119e5n area'
<br /> The watershed model simulates stream bank 14%from
<br /> from
<br /> erosion,
<br /> erosion separately from the individual land 3%i.omi"i 6,2 26'41'
<br /> system mass.6.203
<br /> uses. Loads from stream bank erosion are Figure 8.Sources of Delivered Total Nitrogen(top)and Total
<br /> calculated based on the erosivity of the Phosphorus(bottom)Loads to Falls Lake Based on the Watershed
<br /> stream bank soils, the amount of flow in the Model
<br /> stream and resulting shear stresses, and stream bank stability metrics due to root systems and
<br /> other soil characteristics. The model estimates that during 2014 to 2018, stream bank erosion
<br /> contributed approximately 14 percent of the total phosphorus load delivered to Falls Lake. Because
<br /> nitrogen content is low in the soil, the amount of nitrogen loading from streambank erosion is not
<br /> significant. The Collaboratory has recently funded a study to identify the most likely areas of
<br /> streambank erosion as a result of this modeling and at the request of the UNRBA. This study will be
<br /> extremely helpful in identifying potential stream restoration sites for future investment projects.
<br /> Impacts of Watershed Processes on Delivered Nutrient Loads to Falls Lake
<br /> Based on the data compiled for the UNRBA watershed model, an average of 8.6 million pounds of
<br /> total nitrogen per year were applied or deposited in the watershed in 2014 to 2018. Relative to the
<br /> baseline period of calendar year 2006, this
<br /> amount has decreased by approximately 37
<br /> percent. Most of the nutrients applied,
<br /> deposited, or released to the watershed are Reducing one pound of nutrients in the
<br /> removed from the system by crop harvesting, watershed does not translate to reducing
<br /> denitrification, and other physical, chemical, and one pound delivered to Falls Lake.
<br /> biological processes. During the UNRBA study
<br /> 16
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