Algae And Pollutants: A Disruptive Relationship

Algae are primary producers in aquatic ecosystems, playing a significant role in water pollution. They can be affected by organic pollution, which occurs when large amounts of organic compounds from sources like sewage, urban runoff, and industrial effluents enter water bodies. This pollution can reduce water quality and harm aquatic life.

Algal blooms, which are excessive growths of algae, can be caused by an increase in nutrients like nitrogen and phosphorus from sources such as agriculture, stormwater runoff, and wastewater. These blooms can reduce water quality, harm aquatic life, and create dead zones where there is little to no oxygen, leading to aquatic life death.

Algae are also vulnerable to physical harm from contaminants like heavy metals, oil spills, and pesticides, which can cause deformities and even death. Additionally, certain pollutants can promote the growth of harmful bacteria and algae, which can impede the growth of naturally occurring plants that marine life depends on.

Algae can also act as bioindicators of water quality, as certain species are associated with clean or polluted water. They can quickly respond to changes in the environment and are diverse, making them good indicators of pollution levels.

Overall, algae play a crucial role in aquatic ecosystems, and their disruption by pollutants can have far-reaching consequences.

Algal blooms

Not all algal blooms are harmful, and some are referred to as "nuisance blooms". These blooms are not usually dangerous but can discourage people from visiting beaches, drinking tap water, or eating fish from water with an ongoing algal bloom.

To prevent algal blooms, it is important to limit nutrient pollution in water. This can be done by using fertilizers properly, maintaining septic systems, and reducing the amount of nutrients that get into water from homes and yards.

Direct exposure to algae

Algae are the main primary producers in all kinds of water bodies, and they are involved in water pollution in several significant ways. Firstly, the enrichment of algal nutrients in water through organic effluents may selectively stimulate the growth of algal species, producing massive surface growths or 'blooms' that, in turn, reduce water quality. Certain pollution algae may be toxic to fish and other aquatic life and even humans. Algal blooms can also negatively impact aquatic life by blocking out sunlight and clogging fish gills.

Harmful algal blooms (HABs) can occur in lakes, reservoirs, rivers, ponds, bays, and coastal waters, and the toxins they produce can be harmful to human health and aquatic life. After being consumed by small fish and shellfish, these toxins move up the food chain and can impact larger animals like sea lions, turtles, dolphins, birds, and manatees.

Algae are also good indicators of water pollution since many species occur consistently and predominantly in clean water zones. However, it is more satisfactory to emphasise the presence or absence of several species of clean water algae rather than any one species to define the clean water zone.

Algae are also known to be the cause of tastes and odours in water. Certain diatoms, blue-green algae, and coloured flagellates are the best-known algae to pose such problems in water supplies, but green algae may also be involved.

Algae have an important role in the self-purification of organic pollution in natural waters. Many studies have revealed that algae remove nutrients, especially nitrogen and phosphorus, heavy metals, pesticides, organic and inorganic toxins, and pathogens from surrounding water by accumulating and/or using them in their cells.

Algal blooms can reduce the ability of fish and other aquatic life to find food and can cause entire populations to leave an area or even die.

Dead zones and hypoxia

Dead zones are hypoxic areas in the world's oceans and large lakes, where aquatic life cannot survive due to low oxygen levels. They are generally caused by significant nutrient pollution, especially in bays, lakes, and coastal waters, as they receive excess nutrients from upstream sources. The largest dead zone in the United States, spanning about 6,500 square miles, occurs every summer in the Gulf of Mexico due to nutrient pollution from the Mississippi River Basin.

When a body of water experiences hypoxic conditions, aquatic flora and fauna alter their behaviour to reach sections with higher oxygen levels. Once the dissolved oxygen (DO) level falls below 0.5 ml O2/liter, mass mortality occurs. This is because, at such low DO levels, these bodies of water cannot support aquatic life.

Dead zones can be caused by both natural and anthropogenic factors. Natural causes include coastal upwelling, changes in wind and water circulation patterns, long water residence times, high temperatures, and high sunlight penetration. Anthropogenic causes include the use of chemical fertilizers, direct sewage discharge, and nutrient discharge from large animal waste.

Excess nutrients, particularly nitrogen and phosphorus, inputted into aquatic systems by rivers, ultimately from urban and agricultural runoff, can lead to eutrophication. This results in high productivity, producing organic material that sinks to the bottom and is respired, consuming oxygen and causing hypoxia or anoxia.

The major groups of algae are cyanobacteria, green algae, dinoflagellates, coccolithophores, and diatom algae. An increase in nitrogen and phosphorus generally causes cyanobacteria to bloom. The bacterial degradation of their biomass consumes oxygen, creating hypoxia.

The effects of dead zones on fisheries and marine commercial activities depend on their length of occurrence and location. While dead zones can lead to a decrease in biodiversity and a collapse in benthic populations, they can also cause temporary rises in select yields among pelagic populations due to increased nutrient availability.

The influence of dead zones on coral reef ecosystems is also significant. Hypoxia can lead to reduced photosynthesis and calcification, coral bleaching, and an increase in the abundance of algae and the spread of coral diseases.

Jellyfish can thrive in dead zones, and their blooms can lead to major changes in ocean food webs. Dead zones may serve as breeding grounds for jellyfish populations, as hypoxic conditions drive away competition and common predators.

Hypoxia also affects seagrass beds, causing die-offs and reducing biodiversity. Seagrass is a source and sink for oxygen in the surrounding water column and sediments, and deoxygenation disrupts this balance.

Mangrove ecosystems experience hypoxia more commonly than seagrass beds and coral reefs. Shrimp farms in mangrove forests are considered the greatest anthropogenic threat to these ecosystems, as they reduce water circulation and quality, promoting diel-cycling hypoxia.

Algae as bioindicators

Algae are an important bioindicator of water quality. They can be used to monitor the long–term and short–term status of aquatic environments, including lakes, wetlands, rivers, and estuaries.

Algae are sessile organisms, meaning they cannot avoid potential pollution through migration or other means. They must either tolerate the ambient environment or perish. Algal generation times range from a few days to several months, allowing for the observation of both short- and long-term shifts in environmental conditions.

Algae have species-specific environmental tolerances and preferences, directly responding to water chemistry, such as nutrient levels, salinity, pH, organic pollution, herbicides, etc. They are also species-rich and spatially compact, making them an information-rich system for environmental monitoring.

Algal bioassessment methods can be divided into two main types: field sampling and laboratory analysis. Field sampling methods include semi-quantitative and quantitative sampling. Semi-quantitative sampling is used in the European Union and involves evaluating algal species composition and providing semi-quantitative estimates of species abundance. Quantitative sampling is preferred in the US and involves collecting algal samples from multiple habitats or a single targeted habitat.

Laboratory analysis of algae can be divided into taxonomic analysis and quantification. Taxonomic analysis identifies algal species, while quantification estimates algal density or biovolume. The European standard semi-quantitative method is best suited for taxonomic identification, while quantitative methods are used in the US to accurately assess algal biomass and taxonomic shifts.

Algal bioindicators can be classified into two main types: biotic indices (BI) and multimetric indices of biotic integrity (IBI). BI are derived from semi-quantitative data and evaluate individual stressors, such as organic pollution, nutrient load, and pH. IBI, on the other hand, are multimetric indices that assess the overall ecological condition of streams and rivers.

Algae are particularly useful as bioindicators of nutrient conditions. They can indicate nutrient enrichment, which typically stimulates algal growth, as well as nutrient limitation, which can limit algal growth. Functional responses of the benthic algal community, such as alkaline phosphatase activity and atmospheric nitrogen fixation, can be used to infer nutrient conditions.

In conclusion, algae are valuable bioindicators of stream and river water quality. They provide information about both the structural and functional integrity of aquatic ecosystems and can be used to monitor a variety of environmental variables, including nutrients, pH, and organic pollution.

Algal-bacterial ponds

The algae-bacteria consortium offers a more effective performance in pollutant removal compared to individual algae or bacteria. For instance, the consortium composed of Selenastrum capricornutum and Mycobacterium sp. strain A1-PYR demonstrated a higher degradation efficiency of pyrene than their individual cultures.

The mutualistic interactions between algae and bacteria are based on physical contact, substrate exchange, signal transduction, and horizontal gene transfer. These interactions have a significant impact on the physiology and metabolism of both organisms, ultimately shaping microbial diversity and the balance of aquatic ecosystems.

In algal-bacterial ponds, the photosynthesis of algae provides bacteria with oxygen and organic carbon. In return, bacteria produce carbon dioxide, inorganic nitrogen, and inorganic phosphate, which support the growth of algae. This exchange of nutritional metabolites is essential for the robust growth of both partners and enhances their resilience to environmental fluctuations.

Additionally, bacteria can aid in the reduction of excess organic material and sedimentation that support the growth of pond algae blooms. While bacteria do not directly attack algae, they can help prevent their formation by cleaning the pond and creating a healthy environment. This approach is preferred over the use of algaecides, which have historically been overused and have created more pond-related problems than they have solved.

To optimize the performance of algal-bacterial ponds, robust aeration is crucial. Aerobic bacteria, which utilize oxygen and rapidly break down organic compounds, are more effective when used in conjunction with pond aeration.

Overall, algal-bacterial ponds offer a promising and environmentally friendly solution for wastewater treatment, leveraging the natural synergy between algae and bacteria to enhance the self-purification of water bodies.

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