The Structure of Aquatic Ecosystems Created by Dave Werner MATES

5 Major Elements of Lake Structure  1. Morphometry  2. Physical  3. Chemical  4. Biological  5. Watershed & Airshed

Lakes  1. Morphometry = function of underwater contour lines, the shape of the lake, & its geologic origin.  Lake’s Morphometry is basic to its structure  For example, when we know the shape and structure of a lake basin, we can sometimes predict how weather conditions or human-induced events may affect water levels in that system.  Still lakes = lentic environments  Flowing = lotic systems, streams

2. Light & Temperature  2 major zones: –Littoral –Pelagic or limnetic

Light & Temperature  Light Zonation –Photic/Euphotic Zone –Aphotic Zone/Profundal  Sublittoral Zone = The deepest area of plant growth.

Temperature Zonation  As light energy is absorbed by water, it is converted to heat energy, which results in the warming of the lake-surface water.  During summer, thermally stratified lakes are warmer at the top and cooler at the bottom.  The warm surface layer is called the epilimnion, and the cooler bottom layer the hypolimnion.  The zone of rapid temperature decline in the water column from shallow to deep water is called the thermocline or the metalimnion.  Lines of equivalent temperature (or concentration) = Isopleths (Fig. 2.7a

Fig (pp.41-43)

Factors Affecting Thermal Stratification  Time of Year  Lake Depth  Wind Fetch  Topography  Solutes

Annual Mixing Patterns  Amictic - never mixing, usually ice covered year around, in the polar regions.  Meromictic - lakes that may mix once or more annually, but do not mix completely.  Polymictic - these lakes have many periods of mixing annually, even ap- proaching continuous mixing and are influenced more by daily temperature changes than seasonal.  Monomictic - one period of mixing annually, the cold monomictic lakes are ice covered most of the year and mix during a brief summer, while the warm monomictic lakes are the opposite with a brief ice-free winter period of mixing.  Dimictic - lakes that usually mix twice annually in the spring and in the fall. This category covers the lakes in the temperate zones of our globe and includes the majority of our lakes.

3. Chemical Factors  The depth at which rapid change in a substance occurs.  The Berkeley Pit is a chemically layered system, which means that the chemistry of the water changes with depth. The brownish-red water at the surface is actually the least contaminated water in the pit, and the deeper it gets, the worse the water quality. The color changes as well, going from brownish-red on top to bluish green at the bottom.  At a certain depth, the chemistry of the water changes so rapidly that it forms a chemical boundary scientists refer to as the chemocline (see illustration and graphs). Water above the chemocline is chemically lighter (i.e., less dense) than the water below. The layering of the two waters is like oil floating on water. The water above the line is also less acidic (higher pH), with lower concentrations of metals. The two layers of water (above and below the chemocline) act like fresh water floating on salt water, never mixing unless stirred.

4. Biological Zonation  Plankton  Nekton  Neuston - surface –Pleuston – Large floating assemblages  Attached Algae – Littoral Zone  Aquatic Macrophytes – Higher plants, likely to dominate sandy or muddy littoral zones  Aufwuchs - the small animals and plants that encrust hard substrates, such as rocks, in aquatic environments. Ex: Algae, fungi, bacteria, protozoa.  Benthic/Benthos –Epifaunal –Infaunal

5. Watershed & Airshed  The size, slope, geologic composition, & climate of the lake’s drainage basin influence the identity & quantity of minerals suspended or dissolved in the lake or deposited in the sediment.

Ponds vs. Lakes  Pond – generally smaller than a lake.  Lake – A large inland body of water, fresh or salt. –The Manahawkin Lake can be found on the West Creek USGS quad topo map. Manahawkin Lake is a reservoir in Ocean County in the state of New Jersey. The latitude and longitude coordinates for this reservoir are , and the altitude is 23 feet (7 meters).

Streams & Rivers  River – larger & fast moving, often warmer.  Stream – smaller, usually lead to larger rivers.  These are Lotic systems – defined by water flow. –Discharge (volume per time) –Current (distance per time)

Meandering

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Biological Structure of Streams  Drift – Living benthic invertebrates& algae that have released or lost their attachment to substrate. Optimum food supply for fish & inverts.  Detritus – dead organic fragments coated w/ bacteria, fungi, & small protozoans.

Estuaries  Where the river meets the sea.  Structure is modified by: –Morphometry –Tide –Inflowing FW  Salt Wedge

Salt Wedge  Salt Wedge Animation Salt Wedge Animation Salt Wedge Animation

Wetlands  Marshes, swamps, or bogs  Vegetation = most important structural elements (emergent macrophytes, trees, & Sphagnum moss).