EFFECT OF ALGAL BLOOM ON FRESHWATER ECOSYSTEMS

OUTLINE INTRODUCTION TYPES OF ALGAE CAUSES OF ALGAL BLOOM EFFECT OF ALGAL BLOOM IN FRESHWATER ECOSYSTEMS CONTROL OF ALGAL BLOOM CONCLUSION REFERENCES

INTRODUCTION What is algal bloom? An algal bloom is the rapid increase in the population of algae in an aquatic system over a short period of time. It can occur in fresh as well as in marine environment and is recognized by the discoloration in the water from their pigments Cyanobacteria were mistaken for algae in the past, so cyanobacterial blooms are sometimes also called algal blooms(Huisman et al, 2005). Blooms which can injure animals or the ecology are called "harmful algal blooms" (HAB), and can lead to fish die-offs, cities cutting off water to residents, or states having to close fisheries

INTRODUCTION Algal bloom occurs when there is excessive amount of artificial nutrient enrichment discharged into the water and when environmental factors such as temperature Turbidity Oxygen level Light Are available in the correct amount thereby creating a set of favourable conditions specific for certain algae species for growth and reproduction (Davis et al, 2009).

Fig 1. River Tuhai showing massive algae bloom. Source: Pearl, 2009

TYPES OF ALGAE IN ALGAL BLOOM Algae are small photosynthetic organisms that live suspended just beneath the water surface, they use energy from sunlight and raw materials to make their own food. Four major types of algae are implicated in algal bloom. Green algae( chlorophyta) Diatoms (baccilariophyta) Euglenoid Blue green algae(cyanobacteria)

Fig 2. Types of algae involved in algal bloom. Source: Paerl, 2008 Chlorophyta Euglenoid Cyanobacteria Diatoms

CAUSES OF ALGAL BLOOMS Eutrophication This is referred to as the artificial nutrient enrichment of water bodies . Nutrients promote and supports the growth of algae and cyanobacteria. The main nutrient contributing to eutrophication are phosphorus and nitrogen (Paerl,1997). In the landscape, runoff and soil erosion from fertilized agricultural areas, erosion from land clearing (deforestation) and sewage effluent are the major sources of phosphorus and nitrogen (Paerl,1997).

Slide Title Product A Product B Fig 3. Causes of Alga Bloom . Source : Clean water fund

CAUSES OF ALGAL BLOOMS Increase in temperature: Water temperatures above 25⁰C are optimal for the growth of cyanobacteria and thus have a competitive advantage over other types. Harmful algae usually bloom during the warm summer season or when water temperatures are warmer than usual. Climate change is seen as a factor in increasing the temperature of water bodies (Paerl and Huisman 2008).

EFFECTS OF ALGAL BLOOM IN FRESHWATER ECOSYSTEM Fresh water ecosystem is negatively impacted by algal bloom. The effects includes: Depletion of dissolved oxygen: Bacterial decomposition of dying blooms may lead to oxygen depletion (hypoxia and anoxia), and subsequent fish kills (Huisman et al, 2005). Reduction of water quality Distortion of food chain

EFFECTS OF ALGAL BLOOM IN FRESHWATER ECOSYSTEM Reduced light penetration leading to reduced primary productivity: An over-abundance of algae can block out the light to other plants, such as seagrasses Bioaccumulation along food chain Toxins produced by certain algae can be taken up by a zooplankton and then the toxins may build up within the organism due to slow metabolism . When eaten up by fish, the accumulation continues and thus can lead to food poisoning.

CONTROL OF ALGAL BLOOM Fig 4. Control measures for Algal Bloom. Source: Clean water fund

CONTROL OF ALGAL BLOOM The use of other animals to prey on algal bloom e.g. scallops, sponges, copepods and filter feeding oysters. Dumping of industrial and domestic waste into water bodies should be prohibited and waste recycling encouraged. Legislation should be made against the discharge of waste that promotes the growth of algae.

CONCLUSION Algal bloom results to increased growth in the algal population due to artificial nutrient enrichment leading to effects such as depletion of dissolved oxygen, reduction of water quality, reduced light penetration and others, thereby negatively impacts the freshwater ecosystem.

REFERENCES Paerl HW, Huisman J (2008) Blooms like it hot. Science 320:57–58 Davis TW, Berry DL, Boyer GL et al (2009) The effects of temperature and nutrients on the growth and dynamics of toxic and non-toxic strains of Microcystis during cyanobacteria blooms. Harmful Algae 8(5):715–725 Huisman JM, Matthijs HCP, Visser PM (2005) Harmful cyanobacteria.Springer aquatic ecology series 3. Springer, Dordrecht,The Netherlands, p243

REFERENCES Paerl HW (1997) Coastal eutrophication and harmful algal blooms: importance of atmospheric deposition and groundwater as “new” nitrogen and other nutrient sources. Limnol Oceanogr 42:1154–1165 Paerl HW (2009) Controlling eutrophication along the freshwater–marine continuum: dual nutrient (N and P) reductions are essential. Estuar Coasts 32:593–601 Paerl HW, Huisman J (2009) Climate change: a catalyst for global expansion of harmful cyanobacterial blooms. Environ Microbiol Rep 1(1):27–37