Ecology of ponds : anthropogenic and environmental effects on biodiversity : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Conservation Biology at Massey University, Auckland, New Zealand
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2022
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Massey University
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Abstract
Ponds are a vital component of the freshwater ecosystem but have been understudied worldwide. The paucity of research is especially disturbing due to increasing pressure on freshwater ecosystems. Pond ecosystems are vulnerable due to anthropogenic activities and changing environmental conditions. Ponds are the most ubiquitous freshwater ecosystems found in the Auckland Region of New Zealand. Despite their abundance (occurring in all landscapes) and significant ecological role, there is a lack of knowledge on the ecology of pond ecosystems in New Zealand. Further, literature on the impact of land use/ land cover (LULC) and human population density on pond water quality and biodiversity is lacking globally. I studied aspects of ponds (natural and man-made) ecology in the Auckland region by assessing both abiotic and biotic factors in the summer and winter seasons. Specifically, my study focused on six aspects of the ecology of pond ecosystems: i) the relationship between water quality and LULC at multiple spatial scales across the seasons, ii) the temporal community composition of macroinvertebrates and the relationship between the communities and the abiotic factors, iii) the influence of anthropogenic activities (measured as human population density and as pond types or function) on the macroinvertebrate communities, iv) the phytoplankton communities in ponds across the seasons, v) the limiting nutrient(s) in periphyton biomass in ponds using an in-situ experiment, and finally, vi) a single case study tracking a newly formed pond in a restoration area and development of its macroinvertebrate community over one year.
I sampled 50 ponds in the Auckland region across two seasons (summer and winter) to assess pond water quality (evaluated using seven physicochemical variables: pH, percentage dissolved oxygen '% DO', conductivity, temperature, total dissolved solids 'TDS', salinity, nitrate, phosphate and ammoniacal nitrogen). My aim was to understand the relationship between water quality and the landscape features (physical variables and LULC types: ‘forest, grass, and impervious surface’) at multiple spatial scales (10m, 100m, 500m and pond catchment) from the pond. I found a significant seasonal difference in the water quality of ponds. All the water quality variables measured apart from ammoniacal nitrogen were higher in summer, suggesting that the water was of lower quality at that time. Also, the effect of LULC on the physicochemical water quality parameters varied spatially and seasonally. LULC at the catchment and 500m scale influenced the water quality in winter, while the LULC at 100m affected the water quality in summer. The results highlight the critical and complex role of environmental factors and LULC in determining the water quality in ponds.
I assessed the macroinvertebrate community compositions and water quality in 12 ponds across two seasons for two years. I found an average of 15 macroinvertebrate taxa in focal ponds. Insects were the most diverse group found, although Crustacea were most abundant. The community composition of the macroinvertebrates varied among ponds and varied across seasons and years. Macroinvertebrates were more abundant, and the community was more diverse in summer. The % DO in the ponds was negatively correlated to the macroinvertebrate abundance. My results suggest that macroinvertebrates and water quality in ponds are temporally variable.
I assessed the influence of anthropogenic activities on the macroinvertebrate communities of 11 ponds. Four categories of human population density were used (rural, small urban, large urban, and major urban; in order of increasing human population) to group ponds for analysis. By applying taxonomic and trait-based (functional feeding groups) approaches, I found that high human population density was negatively associated with the macroinvertebrate communities, especially in summer. Ponds in rural areas had the highest diversity of macroinvertebrates and the highest composition of functional foraging group relative to the other areas assessed. This finding suggests that ponds in rural areas had the lowest anthropogenic impact. Ornamental ponds were rich in macroinvertebrates, primarily due to a comparatively more heterogenous pond habitat.
I sampled and analysed the phytoplankton community composition of 12 ponds in summer and winter. Overall, the communities were dominated by taxa in the phylum Chlorophyta (green algae) and class Bacillariophyceae (Diatoms). Although I did find seasonal differences in the phytoplankton communities, these were influenced by temperature and conductivity. In addition, ponds within areas of denser human populations had the most motile diatoms in summer, suggesting high siltation. Despite being moderately polluted, these results show that all ponds generally had healthy phytoplankton communities. Furthermore, by using an in-situ nutrient diffusion experiment, I found that nitrogen is likely to be the limiting nutrient for periphyton growth in ponds.
Finally, I sampled and monitored a newly created and a nearby established pond for a year to obtain insights into the progression of a pond from creation into a functional ecosystem using macroinvertebrates as indicators. I found that Crustaceans were the first to colonise the new pond. The macroinvertebrate community in the new pond was more taxonomically distinct than the established pond at the end of the first year of its creation. Shannon Weiner's diversity index was similar between the ponds, and environmental factors influenced the macroinvertebrate abundance. My results indicate that new ponds can create new habitats and boost local freshwater biodiversity.
By combining water quality analyses, and detailed biodiversity assessment, my thesis demonstrates that pond ecosystems support a high diversity of macroinvertebrates and phytoplankton. Environmental variables, LULC, and human population density influence the biodiversity in ponds, and the extent, relationship, and impact of these are complex and vary seasonally. My study provides new baseline information and valuable insights for future research on pond ecosystems in New Zealand.
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Pond ecology, Water quality, Biodiversity, New Zealand, Auckland