During the summer and fall of 2013, the Merrimack River Watershed Council tested basic water data of the Souhegan River using field equipment (YSI 556) at two sites: Greeley Park Boat Launch in Nashua, NH, and Watson State Park in Merrimack, NH. The YSI instruments test for pH, temperature, conductivity, total dissolved solids (TDS), salinity, and dissolved oxygen. These tests together give us an idea of the overall health of the Souhegan River. MRWC also trained Souhegan Watershed Association staff how to use these instruments in the future. The work was funded by the New Hampshire Charitable Foundation.
- What is pH – pH is a measure of how acid or basic an object is. pH is measured on a scale from 1 (extremely acidic) to 14 (extremely basic). Pure water is neutral, with a pH of 7. During the day, pH levels may change slightly due to biological processes that occur in aquatic ecosystems.
- Why is pH important – Many aquatic animals and plants have adapted to water being at a certain pH. Even slight changes in pH may inhibit species’ reproductive capabilities and cause irritation to the gills of fish and aquatic insects. Very few aquatic organisms can survive if the pH of water is too high (basic) or too low (acidic).
- What influences can cause the pH of our water to change – Polluted precipitation, known as “acid rain”, causes the pH of water to lower. Although this occurs primarily in highly industrialized and urbanized areas, it can occur in any region due to the nature of the water cycle. Dumping industrial pollutants directly into the water and runoff from nearby land influence change in pH significantly.
- Results – In the pH graph, the blue bars represent the testing done at Watson Park in Merrimack, NH and the red bars represent Greeley Park in Nashua, NH. The pH stayed around 7, meaning the water was chemically neutral.
- What is temperature – Temperature indicates how much heat water contains.
- Why is temperature important – Many aquatic organisms have adapted to survive in water within a certain temperature range. Although each species has a different limit, it is important that each species is able to live in water that is suitable for their temperature range. If the water temperature falls outside of this
range, it could affect the specie’s ability to reproduce and survive. The temperature of water affects the amount of oxygen available in the water. As we mentioned earlier, dissolved oxygen is the measure of the oxygen that is available to the water. The warmer the water gets, the less oxygen is available to the organisms in the water; on the other hand, the cooler the water gets, the more oxygen is available.
- What influences can cause the temperature of our waters to change – Industries may contribute to the warming of the water if they are discharging warmer water back into the river or stream. Development may contribute to the warming of water if the trees, which provide shade to the river or stream, are removed.
- Results – In the temperature graph, the blue bars represent the testing done at Watson Park in Merrimack, NH and the red bars represent Greeley Park in Nashua, NH. The hottest month was July.
Dissolved Oxygen (DO):
- What is dissolved oxygen – Also referred to as DO, dissolved oxygen is the amount of oxygen present in the water. Aquatic ecosystems both produce and consume oxygen. Oxygen is produced from the atmosphere and from photosynthesis of aquatic plants and this oxygen is consumed when
aquatic animals use it for respiration and is also consumed during various chemical reactions and decomposition.
- Why is Dissolved Oxygen important – Aquatic animals need a certain amount of dissolved oxygen to be present in order to survive. Many macro-invertebrates (small aquatic insects visible to the eye) require large amounts of DO to be present. If the DO available decreases, these species will not be able to survive, which will in turn disrupt the food chain. Many fish require a specific range of oxygen concentrations. If the amount of oxygen available changes, it could hinder their reproduction and even cause death.
- What influences cause the Dissolved Oxygen to change – Microorganisms, such as bacteria, decompose organic waste. Organic waste can come from many places including: untreated sewage, agricultural runoff, runoff from lawns, and also from naturally occurring materials. In order to decompose the waste, these organisms will consume oxygen in the water. On small levels, the water will be able to replace the consumed oxygen quickly; however, when there are large amounts of organic material in the water the microorganism will consume oxygen faster than it can be replaced. A change in temperature can change the amount of oxygen in the water. Cold water holds more oxygen than hot water. How humans manage land may contribute to temperature changes in water. For example, clearing away trees along the water will reduce the shade which results in the sun directly heating the once shaded, cooler water.
- Results: In the dissolved oxygen graph, the blue bars represent the testing done at Watson Park in Merrimack, NH and the red bars represent Greeley Park in Nashua, NH. The highest month was August but they relatively stayed the same throughout.
- What is salinity – Salinity is the measure of the dissolved salts in water
- Why is salinity important – Aquatic organisms have adapted to thrive in water with a certain level of salinity. Freshwater species have adapted to low levels of salts in the water, while species that live in high salt water environments have adapted to these high level of salts. If a freshwater species is exposed to higher than normal concentrations of salt, they will not be able to survive.
- What influences may cause a change in salinity – The way humans manage their land may contribute to the rise of salinity in freshwater bodies,
such as rivers as lakes. When the riparian zone (the area of land that surrounds the river and is subject to flooding) is cleared, runoff to the river is increased. This runoff may contain a high level of salts, which are carried directly into the river.
- Results: In the salinity graph, the blue bars represent the testing done at Watson Park in Merrimack, NH and the red bars represent Greeley Park in Nashua, NH. The highest month was August for Watson Park and September for Greeley Park.
Total Dissolved Solids (TDS):
- What are total dissolved solids – Total dissolved solids are a measure of the amount of materials dissolved in the water (both organic and inorganic). Total dissolved solids are directly related to water’s conductivity; the more total dissolved solids, the higher the conductivity. The presence of these materials may contribute to the color of the water.
- Why are total dissolved solids important – Aquatic organisms have a certain cell density in which they must maintain in order to keep them
in their correct position in the water column. If water has too few total dissolved solids, the organism may swell because the water may move into the organism’s cells. On the other hand, if the water contains too many total dissolved solids, it may shrink because its cells may lose water.
- Results: In the TDS graph, the blue bars represent the testing done at Watson Park in Merrimack, NH and the red bars represent Greeley Park in Nashua, NH. The highest month was August for Watson Park and Greeley Park stayed about the same throughout.
- What is conductivity – Conductivity is the measure of the ability of water to pass an electrical current. 3 Conductivity is primarily affected by the dissolved minerals, which are determined by the local geology. Each river or stream tends to have a quite constant range of conductivity; and once this rage is established it can be used for comparisons with other conductivity measurements. Any significant changes to the conductivity could indicate pollution along that portion of the river.
- Why is conductivity important – Certain species of fish have adapted to water at certain conductivities. If water falls out of this range, it may affect the ability of a particular species to survive.
- What influences cause conductivity to change – The presence of sewage discharge in water may cause the conductivity to rise due to its presence of certain materials. The conductivity of water may be lowered where oil is present due to oil’s lack of ability to carry an electrical current.
- Results: In the conductivity graph, the blue bars represent the testing done at Watson Park in Merrimack, NH and the red bars represent Greeley Park in Nashua, NH. The highest month was August for Watson Park and Greeley Park stayed about the same throughout.