Algal Blooms
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Introduction:
Algae are a group of single-celled and multicellular plant-like organisms. That means that while algae are technically not plants, they can perform photosynthesis because they have chloroplasts. When environmental conditions are normal, and the ecosystem is in balance, algal growth is kept in check. Algae support and contribute to 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 to favour algal growth this can result in a rapid increase in population size, referred to as a bloom. An algal bloom consists of a layer of algae floating at the surface of the water, which can restrict the amount of sunlight entering the water column. When an algal bloom is present, organisms living further down the water column which rely on sunlight (e.g. animals searching for food visually, or plants using sunlight for photosynthesis) are at a disadvantage, and may be incapable of adjusting. Furthermore, while the increase in photosynthetic algae might suggest an increase in dissolved oxygen, algal blooms actually result in an overall decrease in available oxygen. During the day, while sunlight is abundant, the algae may produce more oxygen. However this increase is not usually enough to counter the increased oxygen demand associated with the organic waste from the dying algae (more living algae, inevitably means more dead algae), and the decrease in oxygen production from aquatic plants that are no longer receiving sunlight.
Blue-green algae (a.k.a. cyanobacteria) are microscopic species of algae found in all bodies of water. Cyanobacteria thrive in slow moving or still waters with high nutrient concentrations, particularly when temperatures are high. While most cyanobacteria pose little threat, a number of species can produce toxins (referred to as cyanotoxins), which can cause serious health effects in humans and animals. Toxins are generally released as the cyanobacterial cell dies and breaks down following a bloom event. The most commonly occurring toxin is microcystin, a hepatotoxin that affects liver function. However, as toxins are only released during bloom events and not every bloom produces toxins, the threat of exposure to microcystin is minimal.
Factors that influence algal growth include increased nutrient concentrations (particularly phosphorus), sunlight, water temperature, and flow. Phosphorus is often the limiting nutrient in freshwater ecosystems as excess phosphorus can promote an increase in biological growth, particularly for strong proliferating species like algae. Human activity is a major source of phosphorus introduced into the water column, which indirectly but strongly links algal blooms to land use and sewage outflow. Flow is another important factor that influences algal blooms. Faster moving water can prevent the harmful buildup of algae on the surface of the water, because it does not have the time to settle. For this reason lakes, ponds and bays are more susceptible to algal blooms than rivers and fast-moving streams. Given the various factors that influence the presence of algal blooms, this indicator can be considered an important way to track climate change.
Despite a solid understanding of what factors contribute to algal blooms, it is still very difficult to predict when and where they will occur. This is why it is important to monitor algal blooms and increase our understanding of them.
Relationships to other indicators:
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.
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.
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.
Further resources:
