Riparian Connectivity
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Introduction:
Natural shorelines play multiple roles in healthy watercourses, such as providing nearshore habitat, filtering runoff from lands, supplying natural nutrients to the aquatic ecosystem, shading watercourses to moderate summer temperatures, stabilizing shoreline soils, and reducing erosion. Fragmentation of the riparian zone creates many adverse effects, which are exacerbated if the riparian zone is hardened, dredged, or used for purposes that release pollutants into the water.
The state of riparian zones can have significant impacts on the quantity and movement (flow) of water. Denaturalized shorelines lined with large rocks or pavement and minimal vegetation allow more rainwater to enter the river, increasing water volume after precipitation events. Natural shorelines featuring a healthy population of native plants have a much greater capacity for absorbing rainwater, thus reducing the amount of excess runoff entering a body of water, helping to avoid sudden and significant changes to flow after a rainfall. Healthy riparian zones can also help to control the rate of flow by stabilizing shorelines and thus maintaining the natural bends and curves in rivers and streams that help to slow the flow rate.
Shoreline vegetation is particularly important for watershed health. Terrestrial and semi-aquatic animals such as frogs and some invertebrates, whose larval or juvenile forms are fully aquatic, will often lay their eggs on or near shoreline vegetation. Aquatic species like smaller fish use near-shore vegetation to hide from and avoid predators. Therefore, loss and fragmentation of natural riparian habitat can have adverse effects on the populations of aquatic and semi-aquatic wildlife. Not only do shoreline plants provide an important physical refuge for smaller animals to hide from predators, they also provide shade, which is instrumental in moderating water temperature when air temperatures rise. Furthermore, the roots of shoreline plants play an important role in absorbing excess water and sequestering excess nutrients and toxins in runoff, thereby preventing contamination of waterways. This helps to control the rate at which essential nutrients like phosphorus are released into the aquatic environment, preventing issues related to nutrient oversaturation such as algal blooms.
Land use can be very tightly linked to riparian condition. When shorelines are repurposed for human use, such as man-made beaches, canals, or large piers, many of the benefits provided by natural shoreline vegetation are lost. Therefore, waterfront property owners – including individuals, businesses, municipalities, etc. – have an important responsibility to keep their shorelines natural as much as possible to help maintain the health of the river and its watershed.
Relationships to other indicators:
Riparian Connectivity
Natural, vegetated riparian areas, the unique, transitional space between aquatic and terrestrial ecosystems, provide numerous benefits including nearshore habitat, filtering runoff, moderating local temperatures, and stabilizing shorelines. Measuring riparian connectivity can provide important information on the health of a watershed and a better understanding of the resilience to threats these areas have compared to shorelines that have been developed.
Algal Blooms
Algae are a group of single-celled and multicellular plant-like organisms. Algal growth contributes and supports the ecosystem in much the same way that plants do, through the production of oxygen and as a potential food source for smaller animals. However, when environmental conditions shift from their normal ranges, this can promote algal blooms, a rapid increase in population size of algae.
Water Temperature
With global temperatures on the rise, water temperature (particularly annual maximum temperatures) will be a crucially important indicator of watershed health moving forward. Water temperature is strongly correlated with a number of other important indicators of ecological status, and can often help to explain, give context to, or even predict changes in habitat quality.
Dissolved Oxygen
Dissolved oxygen (DO) is the concentration of free oxygen in the water column and comes from aquatic plants and algae through photosynthesis, and can also be transferred from the air at the surface of the water. DO is essential for all aquatic life and for the decomposition of organic waste. The amount of available oxygen in the water column is also affected by several abiotic factors including temperature, salinity, pressure and depth, wind, flow, and wave action.
Chlorophyll-a
Chlorophyll-a is used in oxygenic photosynthesis and is the predominant form of chlorophyll in green plants and algae. Measuring the presence of chlorophyll-a in an aquatic environment allows for a better understanding of the density and prevalence of algae which can have an impact on the concentration of dissolved oxygen or likeliness of algal blooms.
Total Phosphorus
Phosphorus is a fundamental building block of life. It has key structural roles in genetic material (eg. DNA) and cellular membranes, and is an active component of cellular energy production, storage, and transfer, meaning many necessary biochemical processes that all living organisms rely on (such as respiration, and nutrient absorption) can only happen if phosphorus is available.
Combined Sewer Overflows
Everytime there is a Combined Sewer Overflow, sewage, along with stormwater is released into a waterbody introducing pollutants, pathogens and excess organic waste. Untreated or inadequately treated sewage poses health risks for people who use the water for recreational activities, such as swimming, paddling, etc. It also impacts aquatic ecosystems as the presence of organic matter, and its decomposition, decreases the amount of dissolved oxygen available.
Flow
How much water or volume of water present at a given time and how quickly it moves along the length of the river determines flow. Flow can provide context to a number of other indicators and as an important measure to factor when examining water chemistry or understanding impact of pollutants (for example, the same concentration of pollution will impact a river with low flow differently than one with high flow). Comparing flow within the same reach can help identify different trends and, when affected by barriers, can impact aquatic biota.
Change in Land Use
Land use is a classification for all the various ways an area of land be used and includes agriculture, urban, roads, natural and harvested forests, wetlands and protected areas. Changes in land use have implications for both the quantity and quality of water introduced to the river through runoff and can help analyse changes in other indicators in proximity to where land use changes have occurred.
Benthic Invertebrates
Benthic invertebrates are the organisms found in soils, rocks and organic materials that make up stream, river, and lake beds. Pollution tolerance varies greatly between different species, so the relative abundances of pollution-sensitive and pollution-tolerant benthic invertebrate species is a good indicator of water quality and ecosystem health.
Invasive Species
Invasive species are non-native species that have been introduced to a habitat and are able to outcompete native species. Invasive species disrupt the established ecosystem which can result in a decrease in habitat quality and health.
Fish Richness
Fish richness is a measure of how many different species of fish are present in an ecosystem or habitat. Generally speaking, higher species richness is better, but some confounding factors include habitat type and the presence of invasive species (which can increase richness while threatening ecosystem health).
Water Mercury
Mercury is highly toxic, but naturally occurring concentrations of it are bound by plants and sediment and removed from the water column. However, human activity introduces excess mercury, resulting in free mercury in the water column. Water mercury is therefore a useful indication of human impact on the watershed.
Ice On/Off
Ice on is the date when a body of water is fully covered by ice, and ice off is the date when the ice disappears from the water surface. These measurements provide information about several environmental conditions, such as air temperature, water temperature, and flow.
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