Ag 508 Aquatic Biology and Environment

Dr. John A. Finn, Room I1, TOB2 (Agricultural and Food Economics building,

opposite old building of Dept of Agriculture)

Email : j.a.finn@rdg.ac.uk

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AG 508 Aquatic Biology and the Environment

Lent Term (January – March 2000)

Convenor: Dr John Finn Room I1 AgEcon email: j.a.finn

Weeks 1&2 : room I1Weeks 3-10: room AG1L04 (New Building)

Week Date

1 13/1 Lecture Course Introduction. Hydrological Cycle and aquaticenvironment.

2 20/1 Lecture Energy flow in streams.

3 27/1 Lecture Floods and disturbances.

4 3/2 Visit Aquatic Weeds Research Unit, Sonning Farm.

5 10/2 Practical 1. River sampling.

6 17/2 Practical 2. River sampling :

7 24/2 Presentations

8 2/3 Lecture Aquaculture 1.

9 9/3 Lecture Aquaculture 2

10 16/3 Assessment. (50%)

Features of Lotic Environments

Lecture Outline Introduction to aquatic habitats

The hydrologic cycle Influences on streamwater chemistry in

lotic environmentsProperties of lotic habitats

Lecture outcomes• List and describe the dominant features of

stream chemistry• Relate the effects of the atmosphere, lithosphere

and biosphere to stream chemistry• Describe main properties of lotic habitats, and

what factors contribute to their variation in time and space.

Why is water important?

•It is the medium by which plant nutrients are introduced into autotrophic plants

•It is an essential part of living tissue

•It serves as a means of thermal regulation for both plants and animals

•It is the medium by which sediments (a prime source of nutrients) are removed or added to ecosystems

•It covers a large proportion of the Earth's surface

•It provides a range of services for humans

Water as a resource Estimated global demand of freshwater:

• 1950: 1360 km3 • 1990 : 4130 km3 • 2000: 5190 km3

Main water uses• Domestic supply• Industrial abstraction• Irrigation• Diversion between catchments• HEP • Transport• Flood control and storage• water transportation• Biological resources• Recreation and culture

The Hydrological Cycle How much water is there?

Whilst estimates vary between 2.5 and 5.8%, only a few percent of Earth's water is fresh. (...take these estimates of fresh water with a pinch of salt...!).

Of global fresh water, about 70% is locked in glaciers, permanent snow and aquifers more than a kilometre deep (such aquifers are generally considered inaccessible). Roughly 30 % of global freshwater remains as accessible groundwater, generally in either groundwater, streams, rivers or lakes.

The average of 30% of accessible freshwater is not stagnant, and is being driven by gravity and solar energy through a continuous cycle of water down from the air as precipitation and back up again through evaporation and transpiration. i.e. The Hydrologic Cycle

The proportion of water that ends up as stream flow depends on:

weather (arid versus temperate regions; evaporation, transpiration, ppt. held as snow or ice)

soil type and development (dry permeable soil vs moist porous soil)

vegetation slope of the land properties of aquifers

Thus, we see that the boundaries of rivers extend much further beyond the air-water interface and the bed of the river/stream.

Streams and rivers do not just get their water from a number of sources, but the water itself has intimate contact with the atmosphere , vegetation, soil, and rocks before entering the freshwater habitat.

Habitat features of lotic environments

What are important chemical descriptors of freshwater?

temperature, pH, dissolved gasses, suspended and dissolved organic matter, suspended solids, dissolved nutrients (N+P) and dissolved ions

What are important physical descriptors of freshwater?• bank width, water depth, substrate size,

substrate depth, flow rate, bankfull height What are important biological descriptors

of freshwater ?productivity (light penetration, temperature), riparian vegetation, organisms, interrelationships between species

(see Allan 1995, Chapter 2; Moss 1998, Chapter 3)

Water in lotic environments

a number of chemical influences act to change the chemical composition to a greater or lesser degree

These influences primarily include: Solute composition of rainwater Catchment geology Catchment vegetation Effects of human activities Volcanic activity

Solute composition of rainwater

Atmospheric CO2 dissolves to form the weak carbonic acid (natural pH of rainwater = 5.64).

Sea spray can increase concentrations of Na and Cl.

Atmospheric pollution: Sulphur dioxide, nitrogen oxides, hydrogen fluoride etc.

Volcanic emissions

Catchment geology

rocks give most of the inorganic substances that reach freshwaters

about 70% of the surface of the continental crust is covered by sedimentary rocks - they are soluble and readily weather

Extent of chemical change by geology is affected by• the amount of precipitation, • availability of chemical substances• local geology and soils of ecosystems• alteration by humans

Alteration of freshwater chemistry by catchment vegetation

Contributes to the formation of soil Provides a source of nitrogen (nitrogen

fixation provides nitrate for plant uptake, and easily leached into streams

Live and dead biomass forms a store of soluble ions (not leached as readily)e.g Hubbard Brook

Provide organic matter that reaches the streams

Fuller vegetation cover reduces erosion, and entry of silt and suspended solids and provides habitat ‘corridor’

Organic matter may enter waters

Increase in evapotranspiration can reduce the amount of water leaving the stream

Effects of human activities

Agricultural nutrients

Agricultural chemicals

Human settlement

Industry

Habitat simplification/modification

Physical properties of the river habitat vegetation linkage between the catchment and terrestrial

biogeochemical cycles. catchment size, stream size and order pattern of water movement affected by

characteristics such as slope, depth and permeability of soils, and local patterns of precipitation.

hierarchical organisation of patterns and processes

Physical properties (substrate particulate organic matter)

Flows and hydraulics• Discharge and current• Flow and sheer stress• Floods

Spatial and temporal variability in physical properties

Factors important to biota of streams and rivers

(Reference: Allan chapter 3)• 1. Current• 2. Substrate• 3. Temperature• 4. Oxygen• 5. Light• 6. Species interactions

We will look at each of these in turn:

1. Current• Benefits and risks• Organisms can be adapted to fast or slow-water

conditions e.g. caddis larvae• invertebrates have anatomical features that prevent

dislodging• velocity affects substrate size resource supply,and

other env. factors

2. Substrate• There are many kinds of substrates• Slower currents correlated with finer particle

size (as well as others)• But it’s not just size that counts!• Substrate can display high variability• Field surveys indicate importance of substrate to

diversity and abundance of biota in lotic habitats

3. Temperature• affects metabolism• can often set limits to geographical distribution • longitudinal temp change in long rivers • variation in temperature is buffered by aquatic

medium• diel, seasonal and geographical variation;

elevation, shading by/removal of vegetation, groundwater

4. Oxygen• Aquatic organisms have several adaptions for

gaseous exchange• Solubility of oxygen in water is related to

temperature• In unpolluted running water, oxygen usually not

limiting• High temperature, low flow, decomposition of

o.m. contribute to oxygen poor conditions. 5. Light

Summary Rivers and streams arise from that portion of the hydrologic

cycle that is surface runoff. Several factors influence the extent of surface runoff: e.g. climate, vegetation

Many factors act to cause considerable variation in water chemistry between running water habitats. e.g. rainwater composition, geology, vegetation, human influences

Water chemistry and other factors can be of importance to the biota of running water habitats (examples include temperature, oxygen, current, substrate type and light)

Next week: Food webs and energy flow in running water habitats

References (for this lecture in brackets) The biology of streams and rivers. 1998. Giller

and Malmqvist. Oxford University Press. (Chapter 1.)

Stream Ecology. Structure and function of running waters. 1995. Allen, J.D. (Chapters 1& 2.)

Ecology of fresh waters. Man and medium. 1988. Moss, B. Blackwell Scientific. (Chapter 3.)

Natural Ecosystems. 1973. Clapham, Jr., W.B. MacMillan. (Chapter on aquatic habitats.)

How many people can the Earth support? Joel E. Cohen. Chapter 14. Water: a Case Study.

Threats to the World’s Water. Maurits la Riviere. Scientific American, September 1989. Pp 48-55.

Websites http://www.execpc.com/~aqsys/index.html Institute of Hydrology:

• www.nwl.ac.uk/ih/www Aquatic life and ecology interests on the

internet (lists about thirty websites):• http://www.geocities.com/RainForest/

Vines/4301/links.html The Environment Agency (Flood relief scheme,

eutrophication, water demand, groundwater contamination):• http://www.environment-agency.gov.uk/

If you find any other websites that are particularly interesting please send me the address so that I can distribute it. Thanks.

Email: j.a.finn@rdg.ac.uk