Pond succession, also known as hydrosere, is the predictable, natural process where an aquatic ecosystem gradually transforms into a terrestrial one over a long period. This continuous change begins when a newly formed pond is a deep, clear body of water, and ends when the basin is completely filled in. The stages of succession represent a slow transition from a purely aquatic environment to a wet meadow, and eventually to a stable forest or grassland. This transformation is driven by biological activity and the constant inflow of materials, making the pond progressively shallower and drier.
The Mechanisms Driving Change
The physical transformation of a pond is primarily driven by two interrelated abiotic factors: sedimentation and eutrophication. Sedimentation occurs as soil, silt, and debris are washed into the pond from the surrounding watershed by rain and runoff, slowly raising the basin floor. This inorganic material acts as a foundation for the organic matter that will accumulate later.
Eutrophication is the continuous enrichment of the water body with nutrients, primarily nitrogen and phosphorus, which fuels biological growth. As aquatic organisms and plants reproduce, die, and decompose, their remains settle at the bottom, creating a nutrient-rich layer of organic muck. This accumulation of decaying biomass accelerates the infilling process and drastically reduces the pond’s overall depth. The combination of external sediment input and internal organic buildup physically converts open water into solid ground.
Early Stages of Aquatic Dominance
The initial phases of pond succession are dominated by species that live entirely within the water column or immediately at the edges of the open water. This stage often begins with a clear, nutrient-poor, or oligotrophic, environment populated by microscopic organisms like phytoplankton and zooplankton. As nutrient levels rise, the pond enters the mesotrophic and then eutrophic state, supporting a greater abundance of plant life.
Submerged plants, such as pondweed, root themselves in the shallow bottom mud where sufficient light can penetrate the water. Floating-leaved plants, like water lilies, soon appear, their broad leaves shading the water surface and inhibiting the growth of submerged species below. Near the shoreline, emergent species like cattails and rushes establish themselves, their roots helping to trap sediment and create a dense, organic mat. The decay of this abundant plant life adds significant organic matter, pushing the pond toward its next stage.
Intermediate Stages of Terrestrial Invasion
As the pond becomes considerably shallower, the soft, waterlogged substrate can support larger, more structurally complex plants, marking the invasion of terrestrial species. This phase transitions the aquatic environment into a dense marsh or reed-swamp, characterized by a thick layer of organic peat or muck. Emergent plants expand their reach, forming a continuous mat across the former open water, which effectively traps more sediment and further stabilizes the ground.
The water table remains high, but the ground is firm enough to support woody, amphibious species like willows and alders, which are often the first small trees to colonize the area. These water-tolerant trees have high transpiration rates, meaning they draw large amounts of water from the substrate and release it as vapor, actively contributing to the drying of the marshy ground. The dense canopy they eventually form shades out the light-demanding marsh grasses and reeds, replacing them with shade-tolerant wetland shrubs. This stage transforms the basin into a wet woodland, often referred to as a carr, with an increasingly solid, organic-rich soil layer.
The Final Climax Community
The end point of pond succession is reached when the former basin is completely filled in and the area is no longer defined by standing water or excessively waterlogged soil. This final, stable ecosystem is known as the climax community, which is in equilibrium with the regional climate and soil conditions. The high organic content of the former pond bottom now supports a terrestrial ecosystem, which is typically a mature forest in regions with sufficient rainfall.
Specific tree species, such as oak, maple, or beech, will dominate, depending on the geographic location and local soil type. In drier climates or areas with poor drainage, the climax community might instead be a grassland or meadow, where grasses and flowering plants form the stable vegetation. At this point, the physical and biological characteristics of the site have fully transitioned from an aquatic habitat to a self-sustaining land environment.