Lake Yale Hydrologic/Nutrient Budgets and Water Quality Management - PowerPoint PPT Presentation

Lake Yale Hydrologic/Nutrient Budgets and Water Quality Management Plans Presentation to the Harris Chain Restoration Council June 2018 Michael J. Perry Lake County Water Authority

Scope of Work The primary objectives of this project are to quantify and rank hydrologic and pollutant loadings to Lake Yale, and to identify potential water quality improvement projects. Conducted field monitoring to collect hydrologic and water quality data for use in developing hydrologic and nutrient budgets and identify opportunities for load reductions. • The hydrologic budgets include inputs from bulk precipitation, stormwater runoff, inflow from interconnected lakes and canals, and groundwater seepage. • The nutrient budgets include inputs from bulk precipitation, stormwater runoff, inflows from interconnected lakes and canals, groundwater seepage, and internal recycling. Conduct a detailed evaluation of sediment characteristics to include physical and chemical characterization of surficial sediments and evaluation of internal phosphorus recycling. Develop bathymetric maps of water and muck depth, along with estimates of water and muck volume. Identify and evaluate water quality improvement projects, and provide recommendations for water quality improvement options.

Lake Yale is a 4,044 acre eutrophic shallow lake with an average water depth of approximately 3.7 m. The TMDL document indicates a drainage basin of approximately 15,394 acres (Fulton, et al., 2003). Surface outflow from the lake occurs periodically through the Yale Canal into Lake Griffin. Discharge rates and water elevations in Lake Yale are partially controlled by a fixed crest weir located in the outfall canal. Lake Yale is classified as a Class III waterbody with designated uses of recreation and propagation of a healthy, well-balanced population of fish and wildlife. The watershed area of Lake Yale is largely undeveloped, consisting primarily of agriculture, wetlands, and natural land.

Previous Studies During 1995, SJRWMD released Technical Publication SJ95-6 titled “External Nutrient Budget and Trophic State Modeling for Lakes in the Upper Ocklawaha River Basin” (Fulton, 1995). This document provides external nutrient budgets for each of the Upper Ocklawaha River Basin lakes and includes drainage basin boundaries, land use characterization, estimation of runoff volumes and loadings, and trophic state modeling to corroborate the identified loading inputs. An additional study was conducted by Fulton, et al. (2003) titled “Interim Pollutant Load Reduction Goals for Seven Major Lakes in the Upper Ocklawaha River Basin” for SJRWMD. This document consists of an expansion of the 1995 study, identifies both hydrologic and nutrient loadings to Lake Yale over the period from 1991-2000, and recommends pollutant load reduction goals to achieve water quality targets in each of the evaluated lakes. Sources included runoff from land uses such as residential, commercial, industrial, mining, open land/recreational, muck farms, pastures, croplands, silviculture, wetlands, and other agriculture. Atmospheric contributions from wet and dry deposition directly on the lake surface were accounted for based upon measurements in the basin.

Previous Studies (cont.) The mean annual total phosphorus load over this period was estimated at 1,432.4 kg. The three major sources for phosphorus were dry deposition (25.94%), precipitation (19.74%), and wetlands (14.59%). In this evaluation, pasture, cropland, feeding operations, and other agricultural activities represented approximately 5% of the annual average phosphorus. Total nitrogen was estimated at 23,078.7 kg/yr, with precipitation accounting for approximately 42% of the total load. Permitted industrial or domestic wastewater sources represented less than 4% of the phosphorus load and less than 2% of the nitrogen load to the lake. This 2003 report forms the basis for the TMDL document titled “Total Maximum Daily Load for Total Phosphorus for Lake Yale and Yale Canal, Lake County, Florida” issued by FDEP, dated August 14, 2003. However, neither of the two TMDL studies evaluated nutrient loadings originating from groundwater seepage or internal recycling, which often exceeds runoff generated nutrient loadings in hypereutrophic lakes. This study is intended to re-evaluate and verify the previously identified inputs, while supplementing the analyses to include shallow groundwater seepage and internal recycling.

Water Level Elevations and Control Water level elevation data have been collected by SJRWMD in Lake Yale from 1959 to the present. Over the available period of record, water levels in Lake Yale have varied from 53.56-60.28 ft, a difference of approximately 6.7 ft, with an overall mean water elevation of 58.04 ft. The observed water level fluctuation in Lake Yale represents a relatively large range for a Central Florida lake.

Water Depth Contours for Lake Yale (March 16, 2015; Water Elevation = 56.24 ft).

Water Level Elevations and Control

Water Level Elevations and Control The most significant structure which controls discharges from Lake Yale is a 24-inch HDPE in an earth berm approximately 50 ft east of CR 452. The current pipe is a replacement for a similar pipe that was washed out during high water conditions from the 2004 hurricane season. The invert of the HDPE culvert is approximately 58 ft which essentially establishes this as the control elevation for the Box Culvert Crossing at SR 452. lake.

Water Level Elevations and Control Yale-Griffin Canal Culvert Crossing at Emeralda Road.

Relationships Between Rainfall and Water Level Water level data were obtained from the historical water level measurements. Annual rainfall data is based on measurements collected at the Lisbon Meteorological Site which is located approximately mid-way between Lakes Yale, Griffin, and Eustis. A relatively good correlation appears to exist between annual rainfall and water level in Lake Yale, with increases and decreases in water level elevations in Lake Yale generally following annual rainfall patterns. Rainfall in recent years has been insufficient to maintain constant water levels in Lake Yale, resulting in an overall decline in water level.

Summary of Available Historical Water Quality Data for Lake Yale

Historical Water Quality Monitoring Sites in Lake Yale

Trends in Total Nitrogen in Lake Yale from 1982-2016 Total nitrogen concentrations have exhibited a moderate degree of variability over time in Lake Yale, with a relatively close agreement between nitrogen concentrations measured by the various agencies. A general trend of increasing nitrogen concentrations is apparent in Lake Yale over the period of record. A jump in total nitrogen concentrations appears to have occurred in Lake Yale during the period from 1996-1998, with measured values before this period ranging from approximately 500-1,200  g/l and nitrogen concentrations following this period ranging from approximately 1,200-3,000  g/l.

Trends in Total Phosphorus in Lake Yale from 1982-2016 Measured total phosphorus concentrations in Lake Yale have been highly variable over time. A general trend of increasing phosphorus concentrations has occurred in Lake Yale over time. A jump in phosphorus concentrations also occurred in Lake Yale from 1996-1998, similar to the trend observed for total nitrogen. Prior to 1996, the majority of total phosphorus concentrations ranged from approximately 5-25  g/l. After 1998, phosphorus concentrations ranged from 20  g/l to approximately 40  g/l during most events.

Trends in Secchi Depth in Lake Yale from 1982-2016 Measured Secchi disk depths in Lake Yale have also been highly variable over time. Prior to 1996, measured Secchi disk depths in Lake Yale generally exceeded 1 m during virtually all of the monitoring events. However, after 1998, the majority of measured Secchi disk depths were less than 1 m, although isolated values in excess of 1 m were observed on occasion. The trend line for the average annual Secchi disk depths indicates a negative slope, suggesting that Secchi disk depths are decreasing in Lake Yale over time.

Trends in Chlorophyll a in Lake Yale from 1982-2016 The observed trends of increases in chlorophyll-a and decreases in Secchi disk depth, beginning in approximately 1994, appear to closely follow the pattern of increasing nutrient concentrations. As chlorophyll-a concentrations increased during the mid- to late-1990s, Lake Yale was converted from a clear, non-turbid oligotrophic lake system to a plankton-dominated, turbid, eutrophic waterbody. The low visibility caused by the elevated algal growth reduces light penetration and limits the ability for submerged vegetation to grow within the lake which provides a continuing feedback mechanism that maintains the altered high nutrient status of Lake Yale.

TN/TP Ratios in Lake Yale from 1982-2016 The TN/TP ratio data suggest that Lake Yale has existed in a phosphorus-limited condition throughout virtually all of the historical monitoring period. The calculated trend line for changes in TN/TP ratios over time has a positive slope which suggests an increase in TN/TP ratios over time. However the trend is not statistically significant.

Trends in Trophic State Index in Lake Yale from 1982-2016