Benthic Pelagic Coupling

The periphyton developed on sediments (or epipelon) may contribute substantially to the whole-lake primary production in shallow water bodies. Turbid lakes seem more productive than clear lakes if phy-toplankton is the only contributor to total annual production. However, the proportional habitat distribution of the primary producers changes under contrasting turbidity and nutrient states, benthic production being highest in clear lakes. Under nutrient-rich conditions, high phytoplankton production in the water column may suppress the epipelic production throughout the year. Lakes with low nutrient supply, in contrast, tend to have low phytoplankton production, clear water, and therefore a high proportion of benthic production throughout the year, with a slight increase of pelagic production in spring or autumn. At intermediate nutrient levels, lakes may shift from epipelon dominance in winter to phyto-plankton dominance in summer (Figure 5).

On the other hand, fish are considered key determinants in shallow lake functioning, not least because of their positive cascading effects on periphyton via feeding on macroinvertebrate grazers (particularly snails), and the consequent deterioration of the light climate for the submerged plants (Figure 6). Direct or indirect positive effects of fish on periphyton biomass have

200-

100-

200-

100-

Epipelon Phyto-plankton

Total Production/ TP

Epipelon Phyto-plankton

Total Production/ TP

Clear, low nutrients ■ Turbid, high nutrients

Spring Summer Autumn Winter

— Turbid, high nutrients •- Clear, low nutrients Potential at intermediate nutrient level

Winter

Spring Summer Autumn Winter

— Turbid, high nutrients •- Clear, low nutrients Potential at intermediate nutrient level

Figure 5 Benthic-pelagic coupling in shallow lakes. Left panel: Comparison of annual estimates of epipelon, phytoplankton, total microalgal primary production and the ratio of total primary production per pelagic TP in a clear and a turbid shallow temperate lake. Right panel: Tentative conceptual model showing the seasonal variation in the relative contribution of epipelic primary production to total primary production in temperate shallow lakes without submerged macrophytes and with different nutrient levels. Reproduced from Liboriussen and Jeppesen (2003) Freshwater Biology 48: 418-431, with permission from Blackwell.

Enhanced macrophyte growth

1 2 3 4 5 6 7 8 Epiphyton biomass (^g Chl-a cm-2 plant)

1 2 3 4 5 6 7 8 Epiphyton biomass (^g Chl-a cm-2 plant)

s7 s

Shallow Lakes Ecosystem

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Grazing invertebrates (ind cm-2 plant surface)

0 5 10 15 20 25 30 35 40 45 50 Fish biomass (g m-2)

Enhanced macrophyte growth

Clear water state plant dominance

Sparse epiphyton

Abundant epiphytic invertebrates

Low/moderate fish biomass

Eutrophication Reproduction Stocking/colonization Piscivore death

Eutrophication Reproduction Stocking/colonization Piscivore death

High fish biomass

High fish biomass

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Grazing invertebrates (ind cm-2 plant surface)

Sparse epiphytic invertebrates

Dense epiphyton

Turbid state phytoplankton dominance

Reduced plant growth

0 5 10 15 20 25 30 35 40 45 50 Fish biomass (g m-2)

Figure 6 Littoral trophic cascade, linking submerged plants to fish via epiphyton and grazing macroinvertebrates, which could mediate the shift from turbid to clear conditions in shallow systems. A high abundance of fish (caused by several processes) would eliminate epiphyton grazers, allowing epiphyton to accumulate on plant surfaces. Consequently, macrophyte loss would occur owing to light limitation, and the absence of macrophytes would allow a turbid state to dominate. Modified with kind permission of Springer Science and Business Media from Burks etal. (2006), Figure 3 (graphs originally published by Jones and Sayer (2003) Ecology 84: 2155-2167).

s7 s

been registered under different environmental conditions. The strength of trophic cascades in the littoral and benthic zones may therefore determine the fate (the maintenance or loss) of the submerged plants.

Project Earth Conservation

Project Earth Conservation

Get All The Support And Guidance You Need To Be A Success At Helping Save The Earth. This Book Is One Of The Most Valuable Resources In The World When It Comes To How To Recycle to Create a Better Future for Our Children.

Get My Free Ebook


Post a comment