Why we test for phosphorous at Harvey Lake
Aug. 26, 2015
(This report is combined from information by the U.S. EPA, state Volunteer Lake Assessment Program, N.H. Dept. of Environmental Services, and my notes.)
Nitrogen and phosphorus are natural elements essential for plant and animal growth in normal amounts, but they are harmful in excess. They are among the top water pollutants nationally, degrading over 100,000 river and stream miles and over 3.5 million acres of lakes, reservoirs and ponds.
Phosphorus is known as "the limiting nutrient." Phosphorus is the substance that limits biological growth due to its short supply with respect to other substances necessary for the growth of an organism. It only takes a small quantity of phosphorus to increase the growth rate of algae.
In general, an increase of phosphorus to a lake initiates a series of events that can lead to deteriorating lake quality. The increase of phosphorus and an adequate supply of sunlight to an aquatic system results in increased productivity. A decrease in water clarity corresponds to an increase of algal cells. As these cells slowly settle into the deeper, darker waters of the lake, the cells die and collect on the bottom. Bacterial decomposition of large quantities of these cells rob the bottom waters of oxygen. Anoxic (devoid of oxygen) water and sediments promote conditions that encourage the recycling of phosphorus back into the water column.
The New Hampshire Department of Environmental Services (NH DES) conducted water quality monitoring of Harvey Lake in 1977, 1990, and 2006 for Lake Trophic Studies. The Volunteer Lake Assessment Program (VLAP) began in 1995 and continues to the present day. The hypolimnion (lower level of the lake) has low dissolved oxygen concentrations (< 1 mg/L) at depths below 4-5 meters during the summer. Secchi disk transparencies (SDT) are also low, ranging from 1.2 to 2.3 meters with a mean of 1.8 meters. Cyanobacteria blooms containing hepatotoxic (damaging to the liver) microcystins in summer have been observed; chlorophyll-a concentrations over this time period range from 5-34 g/L. Total phosphorous (TP) concentrations in the epilimnion (upper level of the lake) range from 12 to 28 g/L with a mean of 19 g/L. Hypolimnetic TP concentrations range from 21 to 65 g/L with a mean of 36 g/L. The higher mean hypolimnetic TP concentrations suggest that there is sediment release of TP during stratification in the summer. Linear regression analysis of water quality data collected since 1995 by NH DES shows that summer composite chlorophyll-a concentrations have significantly (p<0.05) increased by 7.9% from 1995 to 2006. SDT significantly (p<0.05) decreased 4.1% from 1995 to 2006. Both of these measures suggest that water quality has declined somewhat in recent years.
The importance of managing phosphorus in the watershed is the key to protecting the lake itself.
Excess nitrogen or phosphorus can cause too much aquatic plant growth and algae blooms, sometimes choking off waterways and causing toxic or oxygen-poor conditions that can kill fish and other aquatic life.
Harvey Lake is one of 24 lakes in New Hampshire that were studied in 2008 in a study called Total Maximum Daily Load (TMDL), and designated by N.H. DES and the U.S. EPA as impaired for phosphorous content.
In a final report completed in 2011, these 24 lakes were reportedly not meeting criteria for phosphorus and were not supporting the designated uses of Aquatic Life and/or Primary Contact Recreation Use. They are impaired with combinations of chlorophyll-a and hepatotoxic (damaging to the liver) cyanobacteria, and low dissolved oxygen concentration and dissolved oxygen percent saturation.
The standard identified for safe phosphorous levels by EPA is 12 ug/l, and as of the time of the study, Harvey Lake’s level for total phosphorous was in the range of 16 to 33 ug/l, depending on the testing station.
It is the use of that word “impaired” that scares people, especially those looking to buy property on the lakefront. Over the years, I have received calls from people interested in purchasing property on the lake, and they are wary of this lake being “dirty” or “unhealthy.”
First off, Harvey Lake is assigned a surface water classification of B by the State of New Hampshire. Surface water classifications establish designated uses for a waterbody. Class B waters, “shall be of the second highest quality.” These waters are considered acceptable for fishing, swimming and other recreational purposes and may be used as water supplies after adequate treatment.
The TMDL study prepared for the EPA indicates that Harvey Lake must reduce its phosphorous load to come within acceptable standards. However, our lake is considered “low priority.” Harvey Lake is listed as marginally impaired for aquatic life due to low DO saturation. Primary contact recreation is listed as marginally impaired due to hepatotoxic cyanobacteria and severely impaired due to chlorophyll-a levels.
The analysis suggests that the current loads of phosphorus to Harvey Lake must be reduced by 49% overall in order to meet the target in-lake phosphorus value of 12 ug/L. The load allocation puts primary emphasis on reducing watershed phosphorus sources over other sources. It is expected that these reductions would be phased in over a period of several years.
The current TP load to Harvey Lake was estimated to be 139.6 kg/yr from all sources. Loading from the watershed was overwhelmingly the largest source at 121.1 kg/yr (87 percent of the TP load). In particular, TP loading from the largest sub-watershed (Northeast or Tucker Brook) was the highest at 65.3 kg/yr. The sub-watershed drained by the smaller unnamed tributary to the south of the lake (Southern sub-watershed) contributes 26.6 kg/yr while direct drainage to the lake contributes 29.2 kg/yr. Direct precipitation provides approximately 8 percent of the annual TP load or 11.7 kg/yr while internal loading was estimated to contribute 2.4 kg/yr or 2 percent of the TP budget.
Interestingly, septic systems contribute only 4.4 kg/yr or 3 percent of the annual TP budget to Harvey Lake. Removal of all septic sources (installing sewer lines) would likely be costly and would not substantially impact the lake. (The analysis did not account for actively failing septic systems, which have localized impacts on TP and should be addressed as they are discovered.)
EPA recommends the total phosphorous load needs to be reduced to 70.6 kg/yr in order to meet the water quality target of 12 g/L. Therefore, to reduce phosphorous in our lake, EPA recommends concentrating efforts on the watershed itself, meaning fixing erosion and education of homeowners about proper uses of fertilizers, building practices, and erosion techniques along the shoreline.
Harvey Lake’s watershed, according to DES data, is 1,553 acres that is bordered by Route 4 (the Coe Brown playing fields on the north side of Route 4 are not considered part of our watershed) and extends to its main water source around Tucker Brook marsh. The land in the watershed is mostly forest (62 percent, with another 6.8 percent considered woody wetlands) along with 9.5 percent open water, 9.11 percent developed open space, and 4.84 percent developed at low/moderate intensity.
We have 2.42 miles (12,795 feet) of shoreline, consisting of 66 separate properties. The largest shorefront landowner is Coe Brown Academy, which owns 3,045 feet along the shoreline. Low-impact waterfront properties, in addition to Coe Brown, include Harvey Lake Cemetery (145 feet); town-owned dam, (75 feet); town-owned beach/boat ramp (205 feet); Roman Catholic bishop, (280 feet); and two town-owned lots (167 feet and 65 feet). The lake is 21 feet at its deepest spot, with the mean depth 10 feet. DES figures list the surface area of the lake at 105 acres (We have been using Fish & Game’s measure of 116 acres). Our flushing rate is 2.7, which means all the water in our lake (1.3 million cubic meters) leaves the lake nearly three times per year. The lake sits at 613 feet above sea level.
DES considers Harvey Lake a eutrophic lake. Eutrophication is the scientific term for lake aging. A lake naturally fills in over geologic time. From the time a lake is created, the aging or filling-in process begins. The three levels assigned to lakes are oligotrophic (young, low-nutrient lakes), mesotrophic (moderate nutrient enrichment), and eutrophic (high nutrients). This means our lake has high nutrient enrichment, highly productive planktonic growth, extensive aquatic plant beds, much sediment on the lake bed, low dissolved oxygen on the bottom, and is suitable only to warm water fish species. Compare this to both Northwood Lake and Jenness Pond, both of which the state considers mesotrophic lakes. This means they have moderate nutrient enrichment, moderate planktonic growth, and some sediment on the lake bed.
Looking at the phosphorous numbers over the past 10 years, the readings have remained relatively stable, meaning there have been no major spikes. Phosphorous readings 10 years ago, ranged from 0.020 mg/L at the epilimnion (upper) layer at the deep spot to 0.040 mg/L at the outlet. The readings may be stable, but one thing is certain: The levels of total phosphorous in Harvey Lake are much higher than the state median, and they have remained consistently high over the years. (Jenness Pond’s 2014 TP readings were around 10 mg/L.)
NH Zoology Professor James Haney gave the plenary address at the Lakes Congress hosted by the N.H. Lakes Association in May of 2011 in Windham. Dr. Haney indicated that phosphorous levels up to around 9 ug/L are manageable by the lake, meaning that the lake is capable of dealing with the phosphorous with algae production, phytoplankton populations, etc. It is when we get over these levels, there is a TENFOLD increase in problems associated with phosphorous. So up to 9 ug/L, the lake manages the phosphorous, but over this level, the lake becomes overwhelmed and the phosphorous content starts creating some real issues.
Increased phosphorous levels in freshwater, along with other environmental conditions, have been linked to increased phytoplankton (algae) and cyanobacteria cell production, decreased water clarity, increased Chlorophyll-a level, increased turbidity levels, accelerated lake eutrophication, decreased oxygen concentrations, and undesirable shifts in relative abundance of aquatic species.
Phosphorus loading is accelerated through human activities in the watershed. Human and animal waste, residential and agricultural fertilizers, and atmospheric deposition are the major sources of phosphorous. Erosion and sediment transport, including eroding stream banks, roadway runoff, and exposed soil on construction sites are all potential phosphorus sources. High intensity rain events result in untreated stormwater transported from the land and the road network to storm drains and catch basins which discharge directly and indirectly to surface waters.
Erosion is one of the most common ways that phosphorus enters a lake. Watershed activities that promote phosphorus loading by increasing the soil's capacity to erode include: irresponsible tree cutting; removing stumps, bushes and grasses; and increasing the impervious surface area (driveways, parking lots, etc.).
People can help reduce nitrogen and phosphorus pollution in their local waters by using lawn and plant fertilizer sparingly and never before storms, regularly checking and pumping out septic tanks, never dumping plant or animal waste in a waterway, disposing of pet waste in the trash, pumping boat waste to an onshore facility, and planting native plants to prevent nutrient runoff into waterways.
Using 2014 VLAP data, here’s a comparison of Harvey Lake to two of our closest neighbors:
Data Harvey Lake Northwood Lake Jenness Pond
Watershed area 1,553 acres 15,384 acres 1,837 acres
Surface area 105 acres 687 acres 232 acres
Volume 1.3 M cubic meters 8.5 M cubic meters 2.5 M cubic meters
Flushing Rate 2.7 3.9 1.6
Classification Eutrophic Mesotrophic Mesotrophic
Phosphorous Slightly bad Good Cautionary
pH Slightly bad Bad Bad
Dissolved Oxygen Encouraging Encouraging Encouraging
Chlorophyll-a Slightly bad Good Cautionary
2014 test results (from year-end VLAP report)
Chlorophyll-a Stable Stable Stable
Conductivity Stable Stable Improving
pH (epilimnion) Stable Stable Stable
Transparency Worsening Stable Worsening
Phosphorous Stable Stable Stable
Our most recent VLAP testing, completed by Karen Smith on July 12, 2015, showed our Total Phosphorous levels at 15.3 ug/l at the deep spot epilimnion, 22.5 ug/l at the deep spot hypolimnion, and 21.6 ug/l at the outlet. The inlet testing on Harmony Road could not be performed this session because a beaver dam located upstream had reduced the water flow to negligible levels. Comparing these figures to last year and 10 years ago:
Testing site 7/12/2015 2014 Average 2005 Average
Harmony Road Inlet n/a 33 ug/l n/a
Harvey Lake Road Outlet 21.6 ug/l 27 ug/l n/a
Deep spot – epilimnion 22.5 ug/l 16 ug/l 27 ug/l
Deep spot – hypolimnion 15.3 ug/l 21 ug/l 40 ug/l