SMALL LAKES, PONDS, & SEDIMENTS

Small Ponds

Most common form of limnetic environment, typically found in depressions within lowland areas, accumulating organic and mineral sediments.

Shallow Lakes

Often dominated by macrophytes, with submerged macrophytes establishing themselves in water providing protection from disturbances.

Role of Macrophytes in Shallow Lakes

Sequester nitrogen and phosphorus, provide refugia for large zooplankton, offer surface areas for periphyton growth, release compounds inhibiting phytoplankton, and cause large fluctuations in daily oxygen levels and pH.

Role of Phytoplankton in Shallow Lakes

Can dominate by shading out submerged macrophytes under high nutrient loads, survive well in high turbidity, and thrive in environments lacking refugia for zooplankton.

Smooth Response (Ecosystems)

A gradual adaptation of an ecosystem to changes in conditions.

Abrupt Response (Ecosystems)

Sudden shifts in ecosystem stability due to external changes.

Warming Effects on Lakes

Leads to more mineralization and higher temperatures, giving cyanobacteria competitive advantages, which results in more small fish and enhanced nutrient recycling.

Nutrient Levels and Climate Change

Changes in precipitation alter nutrient loading rates, leading to increased algal biomass, less grazing on phytoplankton, reduced large zooplankton, and often a shift to turbid systems dominated by phytoplankton.

Organic Sediments

Decomposed material from living organisms found in sediments.

Particulate Mineral Sediments

Includes carbonates, clays, and silicates found in sediments.

Inorganics of Biogenic Origin

Such as frustules, scales, and calcium carbonate deposits found in sediments.

Sediment Focusing

A process involving resuspension and turbidity currents that concentrates sediments.

Dy (Sediment Classification)

Slightly acidic, organic-rich sediments where the carbon to nitrogen (C:N) ratio is greater than 10.

Gyttja (Sediment Classification)

Sediments characterized by neutral pH and organic content below 50% with a carbon to nitrogen (C:N) ratio below 10.

Decomposition in Sediments

Rates vary among organic compounds, with carbohydrates and amino acids decomposing faster than humic compounds and lipids, largely driven by bacterial activity in anaerobic metabolism stages including methanogenesis and sulfate reduction.

Sediment Biogeochemistry

Involves processes like organic intermediate transfers and competition between sulfate-reducing bacteria and methanogenic bacteria based on available electron donors and acceptors.