the Loon Flyer Winter 2000
Published by the Squam Lakes Association
Rainfall... People... and Lake Water Quality
Submitted By: Dr. Alan L .Baker, Professor of Aquatic Ecology, University of New Hampshire
High quality lakes will always remain an invaluable attraction to people, thus an important element of New Hampshire's economy. Questions about changes in water quality and clarity are often asked. Now data which have been gathered by University of New Hampshire researchers, in cooperation with many volunteer monitors, are beginning to provide some answers to questions such as: Have our lakes degraded in this century? Is water quality currently deteriorating? And what is causing changes to occur? Now we can begin to answer these questions.
In order to understand the answers, one must have some awareness of Limnology - the study of the geologic, physical, chemical and biological dynamics of lakes. It is important to be alert to the changing nature of lakes, their sensitivity to disturbances, and their likelihood to degrade or improve in quality in response to poor or good protection strategies.
It is possible to identify many characteristics that determine the uniqueness of each lake and help to distinguish a blue jewel from a septic waste depot. Volunteer monitors from the N.H. Lakes Lay Monitoring Program (LLMP) have amassed data from more than 100 New Hampshire lake sites over the past decade. The objective of this effort, established in 1978, was to develop information to scientifically document long-term trends in water quality.
It is now possible to understand the kinds of disturbances that modify the characteristics of a lake for better or worse. This cooperative effort between lakeshore property owners and UNH researchers has established how lake water quality changes over the decades. Based upon accumulated data it is possible to use a model to predict these events.
Although each New Hampshire lake is unique, and there is a diversity of lake types in the state, the LLMP data reveal a remarkably common pattern in the "behavior" of most lakes. Researchers anticipated that multiple sites within any given lake would have the same characteristics. There is also strong evidence that large and small lakes follow a similar pattern of changes, within the ice-free period of a single year as well as through nearly two decades of observations. This is quite a surprise! How can unique lakes in unique watershed "behave" in such a similar manner?
The "long-term" changes in water quality characteristics are not always monotonously negative, but appear to fluctuate corresponding to 11-year cycles of solar flares or sunspots. What is the role of human behavior? There is no cyclic pattern to human activity on lakes.
Why, for example, did Squam Lake become greener from 1979 through 1984, then suddenly clarify in 1985? Why did the clarity of nearly all lakes in the LLMP program improve in 1985? Why did chlorophyll (the major pigment in microscopic plants) decrease significantly in the same year? Furthermore, why was total phosphorous in the water very low in 1985? Why was there a relatively high Acid Neutralizing Capacity in that year? (ANC is the capacity of a lake to absorb or buffer higher levels of acidity in the water). Finally, why have all these water quality parameters increased again from 1986 to 1993?
A few lakes have "misbehaved" and followed opposite trends during the same period, but this can be attributed to their unique characteristics, and to site-specific circumstances.
New Hampshire is a relatively small state. Despite other diversities, our lakes are all subject to the climate we enjoy at 43o to 44o North latitude. The whimsical nature of New England weather, difficult to predict, variable from season to season and year to year, is well known. Could it be that our lakes are responding to climatic variation and global warming? What was unique about 1985?
A reasonable hunch was that changes in total rainfall could be the "pied piper" playing the tune to which the lakes have danced. A comparison of rainfall data from 30 National Oceanographic and Atmospheric Administration weather stations confirmed that the state is basically a single climate region. While rainfall is much higher in some areas than others, the pattern is similar no matter where one looks. A dry year is a dry year and a wet year is a wet year, statewide. The record rainfall between July 1984 and June 1985 occurred during a period of sub-normal rainfall relative to 30-year averages.
So! We have a clue.
The majority of New Hampshire's lakes are what is known as "nutrient limited." This means that certain nutrients, especially phosphorus and nitrogen, when present in lake water stimulate high levels of growth in microscopic aquatic plants such as algae and phytoplankton. Humans, along with other creatures, process these nutrients quickly and deposit them in lakes or in water flowing down a watershed.
In addition, most watersheds in New Hampshire are small and have steep topography. The streams within these watersheds are typically short and fast-flowing, delivering rainwater to lakes very quickly. Thus, episodes of high rainfall deliver more nutrients by washing them into lakes from watersheds. Prolonged periods (up to one year) of high rainfall lead to more nutrient loading and higher total phosphorus levels, therefore greener and less transparent lakes. In addition, sulfur dioxide in rainwaterthe ingredient that causes acid rain and solutes (dissolved acids) collected within the watershed lowered the ANC of our lakes, and the capacity of lakes to buffer the effects of acidity was diminished.
At its present state of development, the LLMP model suggests that the total volume of rainfall is the cause of both seasonal and long-term annual changes in lake water quality throughout New Hampshire. Most lakes "improved" in dry years such as 1985 and "degrade" in wetter years such as 1984 and 1986. The model works to the extent that the loading of nutrients into nutrient-deprived lakes is dependent on rainfall, and this appears to be the case.
Further verification of the model comes from the few more productive lakes, i.e., those higher in naturally occurring levels of nutrients. The "richer" in nutrients a lake is, the "greener" it tends to be. Such "rich" lakes tend to be "diluted" by the loading of stormwater running off the watershed. This again directly implicates rainwater as the "pied piper" which causes such lakes to be somewhat less productive, therefore "improved," during wet years.
At least two important predications can be developed when interpreting the LLMP model. First, changes in rainfall volume associated with global climate change will influence lake water quality directly. If New Hampshire becomes drier, the lakes will tend to remain transparent and on that basis, will likely "improve" in water quality. Otherwise, a wetter future will likely deplete water quality to some extent.
Second, the model provides substantial evidence that our lakes are sensitive to changes in nutrient loading. Such loading can be controlled to a large extent by the choices people make with regard to activities within a watershed area. Such activities include land use and development patterns and practices within the watershed area, as well as along the shoreland areas of lakes and streams. Human activity on the water can also have some impact on nutrient loading of lakes.
Efforts to minimize nutrient loading can make a difference. Such practices as:
· routine pumping of septic systems;
· erosion control;
· maintaining buffer and wooded areas near lakes and within a watershed and;
· control of storm water run-off from roof tops, impermeable driveways and parking lots all help to minimize nutrient transport to lakes.
While we can predict lake water quality parameters based upon weather patterns in a given year or over a period of years, there are a number of issues that require more comprehensive and thoughtful policy development if New Hampshire's lakes are going to remain the blue gems that we take for granted. Here are some of the unresolved issues:
· The survival of each lake given the multiple uses which they receive now, and will receive in the new millennium;
· The study of lake capacity, or use beyond which a lake becomes undesirable;
· The possibility that lakes will lose their aesthetic and economic values if they visibly degrade over time and;
· The establishment of a comprehensive statewide lake use plan to manage our lakes effectively.
STAFF NEWS
We have a new Operations Manager, Rachel Brooker who started on January 10, 2000. Rachel has been vacationing in the lakes region since she was a child and in 1993 she and her husband purchased a second home on Lake Kanasatka in Moultonboro. In 1999, the Brookers decided to relocate to Moultonboro from Virginia. Rachel comes to us after a distinguished 17-year career at the US Department of Defense National Imagery and Mapping Agency. Rachel is the current president of the Lake Kanasatka Watershed Association and is active in the Friends of the Moultonboro Library and the Moultonboro Historical Society. Both Rachel and the SLA staff are excited about her joining our team.