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State of Green Bay: Impairments from Total Phosphorus and Total Suspended Solids

State of Green Bay. Largest of lake's bays at 120 mi length, but much shallower, warmer and eutrophicFlushing time Lake Michigan 99 yrs.Green Bay < 1 yr.Fox-Wolf River basin contributes the largest proportion of pollutants to the lake26% of TP tributary load 57% of PCB tributary load 44% of total Hg tributary loadWater quality status - poor grading to good.

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State of Green Bay: Impairments from Total Phosphorus and Total Suspended Solids

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    3. Green Bay’s Trophic Gradient Hypereutrophic conditions in the southern bay (AOC), meso-trophic conditions in the middle bay, oligotrophic conditions in the northern bay, similar to the lake Trophic Indicators in lower Bay TP – Status poor TSS – Status poor Chlorophyll – Status poor Water clarity – Status poor NH3 – water column meets standards but toxicity in sediments

    4. GBMSD Sampling Stations

    6. Lower Green Bay Chlorophyll a (Algae) Chlorophyll a concentrations have only been measured in Green Bay on a routine monthly basis since 1990. The RAP target concentration for chlorophyll a of 13 ug/l to 32 ug/l is still being exceeded (see graphs). In all zones, chlorophyll a concentrations have significantly decreased since zebra mussels were introduced into Green Bay (p<0.0001). In zone 1, average chlorophyll a concentration decreased by 30% from 69.44 mg/m3 pre zebra mussels to 48.53 mg/m3 post zebra mussels. Zone 2 had a 39% decrease in the average chlorophyll a concentrations from 29.92 mg/m3 pre zebra mussels to 18.17 mg/m3 post zebra mussels and in zone 3 average chlorophyll a concentration decreased by 48% from 14.43 mg/m3 pre zebra mussels to 7.56 mg/m3 post zebra mussels.   There is a well established relationship between chlorophyll a and phosphorus. This relationship exists because phosphorus is a required nutrient for algal growth; if phosphorus concentrations decrease then the amount of chlorophyll a in the system will also decrease. However, zebra mussels may impact this relationship through filter feeding and removing algae. This effectively results in a decreased chlorophyll a concentration without a reduction in nutrients. A recent analysis of the data set by Qualls (2003) revealed that zebra mussels did not change the expected chlorophyll-phosphorus relationship in zones 1 and 2, but did change it in zone 3. It follows that any phosphorus reduction across all zones may not lead to an accompanying drop in chlorophyll a in zone 3, which would be apparent in zones 1 and 2.   Models suggest that a decrease in total phosphorus to100 ug/L (Figure 9 of 93 state of the Bay) would results in a chlorophyll a value of 30 ug/L and a reduction in blue-green algae of about 50 percent. A greater reduction of phosphorus, say to 50 ug/L, would lead to a water column chlorophyll a level of 13 ug/L. Chlorophyll a concentrations have only been measured in Green Bay on a routine monthly basis since 1990. The RAP target concentration for chlorophyll a of 13 ug/l to 32 ug/l is still being exceeded (see graphs). In all zones, chlorophyll a concentrations have significantly decreased since zebra mussels were introduced into Green Bay (p<0.0001). In zone 1, average chlorophyll a concentration decreased by 30% from 69.44 mg/m3 pre zebra mussels to 48.53 mg/m3 post zebra mussels. Zone 2 had a 39% decrease in the average chlorophyll a concentrations from 29.92 mg/m3 pre zebra mussels to 18.17 mg/m3 post zebra mussels and in zone 3 average chlorophyll a concentration decreased by 48% from 14.43 mg/m3 pre zebra mussels to 7.56 mg/m3 post zebra mussels.   There is a well established relationship between chlorophyll a and phosphorus. This relationship exists because phosphorus is a required nutrient for algal growth; if phosphorus concentrations decrease then the amount of chlorophyll a in the system will also decrease. However, zebra mussels may impact this relationship through filter feeding and removing algae. This effectively results in a decreased chlorophyll a concentration without a reduction in nutrients. A recent analysis of the data set by Qualls (2003) revealed that zebra mussels did not change the expected chlorophyll-phosphorus relationship in zones 1 and 2, but did change it in zone 3. It follows that any phosphorus reduction across all zones may not lead to an accompanying drop in chlorophyll a in zone 3, which would be apparent in zones 1 and 2.   Models suggest that a decrease in total phosphorus to100 ug/L (Figure 9 of 93 state of the Bay) would results in a chlorophyll a value of 30 ug/L and a reduction in blue-green algae of about 50 percent. A greater reduction of phosphorus, say to 50 ug/L, would lead to a water column chlorophyll a level of 13 ug/L.

    7. Lower Green Bay Total Suspended Solids

    8. Lower Green Bay Secchi Depth (Water Clarity)

    9. State of the Bay Indicators Trophic state (TP, TSS, NH3, chlorophyll, water clarity) Chemicals of concern (PCBs, Hg and other toxins) Drinking water Fish consumption advisories Fish populations Benthic Macroinvertebrates Aquatic nuisance species Waterfowl use Coastal wetlands Beach closures Recreational Use (boat registrations and fishing licenses) Land Use

    10. Great Lakes Water Quality Agreement Restore chemical, physical and biological integrity of Great Lakes ecosystem Identify “Areas of Concern” geographic areas where Great Lakes beneficial uses are prohibited or impaired Enlist States and Provinces to prepare and implement Remedial Action Plans

    11. Impaired Uses due to TP and TSS in Lower Green Bay Nuisance and harmful algal blooms (blue-green algae) Poor aesthetics, closed beaches Lost tourism, lower property values Taste and odor problems for drinking water DO fluctuations, hypolimnetic anoxia Ammonia toxicity in sediments Poor water clarity, loss of SAV Altered food webs, degraded benthic, fish and wildlife communities In freshwater systems, phosphorus is the essential plant nutrient that is most limited. When phosphorus is abundant, primary production of algae increases to nuisance/harmful levels. Annual loads of TP about 500 MT resulting in summer average water concentrations of > 200 ug/l.In freshwater systems, phosphorus is the essential plant nutrient that is most limited. When phosphorus is abundant, primary production of algae increases to nuisance/harmful levels. Annual loads of TP about 500 MT resulting in summer average water concentrations of > 200 ug/l.

    12. Waterfowl Historically, Green Bay was an important migratory stopover Half million ducks harvested per year in market hunting era 1997 maximum daily count on lower Green Bay was 40,000 diving ducks

    13. Number of ducks, particularly diving ducks, seriously declined from the 1960s through the 1980s A 1977 US FWS Estuary Study concluded the bay had become food limited for migrating waterfowl due to declining benthic invertebrate populations and the loss of submerged aquatic vegetation

    14. Suspended solids and algae limit sight-feeding predator fish

    15. Before 1985, 600,000 cubic yards dredged every year to maintain navigation channel In recent years, only 85,000 to 100,000 cubic yards of sediment is dredged every year Before 1985, approximately 600,000 cubic yards of sediment were dredged every year to maintain a navigation channel. In 1993, the maintenance-dredging target was 400,000 cubic yards. The lower volume was necessitated by inadequate storage space for dredging spoils disposal. In more recent years only 85,000 to 100,000 cubic yards of sediment is dredged every year by the Corps (Dean Haen, Port of Green Bay, Brown County Port and Solid Waste Department). Assuming that 100,000 cubic yards of sediment needs to be dredged each year, the amount of sediment for disposal over 10 years is one-million cubic yards. At a cost of $14 per cubic yard (Great Lakes Water Quality Board Dredging Register), the total cost for dredging and disposal over 10 years would be $84 million. Clearly, investment in best-management land-use practices has dividends beyond the conservation of soil. Before 1985, approximately 600,000 cubic yards of sediment were dredged every year to maintain a navigation channel. In 1993, the maintenance-dredging target was 400,000 cubic yards. The lower volume was necessitated by inadequate storage space for dredging spoils disposal. In more recent years only 85,000 to 100,000 cubic yards of sediment is dredged every year by the Corps (Dean Haen, Port of Green Bay, Brown County Port and Solid Waste Department). Assuming that 100,000 cubic yards of sediment needs to be dredged each year, the amount of sediment for disposal over 10 years is one-million cubic yards. At a cost of $14 per cubic yard (Great Lakes Water Quality Board Dredging Register), the total cost for dredging and disposal over 10 years would be $84 million. Clearly, investment in best-management land-use practices has dividends beyond the conservation of soil.

    16. Monitoring and research of lower Green Bay over the past several decades has revealed that a relationship exists between phosphorus concentrations, Secchi depth, total suspended solids and chlorophyll a concentrations.   Based on these relationships, preliminary targets or objectives for phosphorus, total suspended solids and chlorophyll a were established in the lower Green Bay and the Fox River RAP Update, 1993 (Table) with the objective of achieving sufficient water clarity to meet state swimming beach standards (Secchi depth, 1.3 m) and the minimum light conditions required to support survival of a submergent rooted plant (water celery, Secchi depth 0.7 m). These plants form the basis of an important near shore (littoral) community that had virtually disappeared from the inner bay and the river (AOC) but is showing slight signs of recovery. Unfortunately, the AOC is still not meeting any of the RAP objectives for these indicators (see individual indicators below) as present monitoring data reveals. Monitoring and research of lower Green Bay over the past several decades has revealed that a relationship exists between phosphorus concentrations, Secchi depth, total suspended solids and chlorophyll a concentrations.   Based on these relationships, preliminary targets or objectives for phosphorus, total suspended solids and chlorophyll a were established in the lower Green Bay and the Fox River RAP Update, 1993 (Table) with the objective of achieving sufficient water clarity to meet state swimming beach standards (Secchi depth, 1.3 m) and the minimum light conditions required to support survival of a submergent rooted plant (water celery, Secchi depth 0.7 m). These plants form the basis of an important near shore (littoral) community that had virtually disappeared from the inner bay and the river (AOC) but is showing slight signs of recovery. Unfortunately, the AOC is still not meeting any of the RAP objectives for these indicators (see individual indicators below) as present monitoring data reveals.

    17. Total phosphorus loads for the Fox-Wolf basin including Duck Creek

    18. The current phosphorus loadings from the Fox-Wolf basin to Green Bay and the AOC is approximately 500 mt/yr -1(500,000 kg/yr). Tributaries from the rest of the Green Bay basin discharge roughly 300 mt/yr -1 (300,000 kg/yr) of phosphorus into the bay. Therefore, the total phosphorus loading from the entire Green Bay Basin is roughly 800 mt/yr -1 (800,000 kg/yr), with 63% of the phosphorus load coming from the Fox River. The phosphorus load from Lake Winnebago constitutes over half (52 percent) of the total tributary load delivered from the Fox River. Phosphorus mostly enters waterways from two sources. Nonpoint sources are those that cannot be traced to one individual point of origin, such as agricultural and urban runoff or atmospheric deposition. It is estimated that seventy-three percent (73%) of the total phosphorus entering Green Bay from the Fox-Wolf Basin comes from non-point sources, mostly agricultural (TMDL draft report, 2005). This 73% includes 40% of the Lake Winnebago portion and all of the Duck Creek portion (figure). Municipal and industrial point sources combined account for roughly 27 percent of the total phosphorus load.The current phosphorus loadings from the Fox-Wolf basin to Green Bay and the AOC is approximately 500 mt/yr -1(500,000 kg/yr). Tributaries from the rest of the Green Bay basin discharge roughly 300 mt/yr -1 (300,000 kg/yr) of phosphorus into the bay. Therefore, the total phosphorus loading from the entire Green Bay Basin is roughly 800 mt/yr -1 (800,000 kg/yr), with 63% of the phosphorus load coming from the Fox River. The phosphorus load from Lake Winnebago constitutes over half (52 percent) of the total tributary load delivered from the Fox River. Phosphorus mostly enters waterways from two sources. Nonpoint sources are those that cannot be traced to one individual point of origin, such as agricultural and urban runoff or atmospheric deposition. It is estimated that seventy-three percent (73%) of the total phosphorus entering Green Bay from the Fox-Wolf Basin comes from non-point sources, mostly agricultural (TMDL draft report, 2005). This 73% includes 40% of the Lake Winnebago portion and all of the Duck Creek portion (figure). Municipal and industrial point sources combined account for roughly 27 percent of the total phosphorus load.

    20. The current suspended solids load at the mouth of the Fox River for water years 1995-1999 was 132,000 tons/yr (119,400 mt/yr -1) (TMDL draft report 2005). This amounts to 360 tons per day (327 mt/day) in an average year or is equivalent to 24 dump trucks per day of sediment deposited into Green Bay (link to dump truck graphic). However, approximately 60% of the load is delivered in a much shorter period of time (13-15 days), primarily in spring. The current suspended solids load at the mouth of the Fox River for water years 1995-1999 was 132,000 tons/yr (119,400 mt/yr -1) (TMDL draft report 2005). This amounts to 360 tons per day (327 mt/day) in an average year or is equivalent to 24 dump trucks per day of sediment deposited into Green Bay (link to dump truck graphic). However, approximately 60% of the load is delivered in a much shorter period of time (13-15 days), primarily in spring.

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