Groundwater Research Impact Report, Pūrongo Pānga Rangahau Wainuku 2023

In Aotearoa New Zealand, nearly half of drinking water comes from groundwater, and it is an important source for replenishing surface water like rivers, lakes, and wetlands. This report highlights ESR’s work to understand the current state of groundwater, how groundwater will respond to stressors, and how to prevent groundwater contamination.

Legal frameworks for the conservation and sustainable management of groundwater ecosystems

Groundwater is the largest and oldest continental habitat and is a vital resource for society. This chapter provides a critical review on the existing legal frameworks for the conservation and sustainable use and management of groundwater ecosystems and its related services. Groundwater is mainly perceived as an essential source for drinking water, irrigation, and use in industry, rather than a living entity with a hidden biodiversity that provides essential functions and processes. In fact, groundwater habitats harbor a vast diversity of microbial and metazoan species, of which some are shared with adjoining surface ecosystems, but the majority is unique to the subsurface aquatic ecosystems. Many groundwater species are rare and endemic, with numerous cryptic and relict species, as well as some classified as “living fossils.” It is estimated that >50% of groundwater biodiversity still awaits discovery. Legal frameworks in place are mainly dedicated to protecting groundwater as a resource but largely ignore biological communities and their important functions, which are crucial for maintaining high-quality groundwater and healthy ecosystems, including those on the surface (e.g., groundwater dependent ecosystems). Protection of groundwater ecosystems is often indirect via the resource approach or because valuable groundwater sources overlap with protected land, as part of national parks and nature world heritage areas. However, there are a few exceptions. A strong focus is on Europe and Australia, but further international and national legal aspects of groundwater ecosystem protection are introduced. Current limitations, challenges, and needs are discussed. Groundwater ecosystems are an essential part of the hydrological cycle and deserve similar attention with respect to survey, assessment, and protection in line with surface aquatic ecosystems. Their low resistance to perturbation and high levels of endemic species in very fragmented habitats warrant even stronger protection efforts.

Microbial diversity and processes in groundwater

A large fraction of the total global prokaryotic biomass lives in the groundwater-saturated zones of the continental subsurface. Groundwater environments are dark, and typically contain low levels of organic matter and nutrients. While these environments are locally often relatively stable over time, there can be large hydrological and physicochemical variation across space. Microorganisms catalyze essential biogeochemical processes in groundwater environments, like the cycling of carbon, nitrogen, and other elements, as well as the natural attenuation of contaminants. Instead of operating in isolation, different functional groups of microorganisms interact to drive these processes. In this chapter, we will discuss how microbial diversity and community composition is shaped by the characteristic features of groundwater environments, the importance of microbial interactions in sustaining community diversity and key biogeochemical cycles, including the attenuation of contaminants (i.e., aromatic hydrocarbons, chlorinated organic compounds, toxic metals, and organic micropollutants), and their responses to environmental perturbations.

Exploring the Bacterial Community in Aged Fecal Sources from Dairy Cows: Impacts on Fecal Source Tracking

This paper discusses the impact of agricultural activities on stream health, particularly in relation to dairy cow fecal pollution. The study explores the fecal microbiome of cattle and the potential ecological implications of aging fecal pollution on waterways. The study examines changes in the bacterial community available for mobilization from in-situ decomposing cowpats and the effects of simulated rainfall. The microbiome of individual cowpats was monitored over 5.5 months. We used 16S rRNA metagenomics and machine learning software, FEAST (Fast Expectation-mAximization for microbial Source Tracking), for bacterial and fecal source assignments. The phyla Bacillota and Bacteroidota are dominant in the fecal microbiota of fresh cow feces but shift to Pseudomonodota, Actinomycetota, and environmental Bacteroidota in aged cowpats. Potential impacts of these bacterial community shifts on inputs to local agricultural streams are discussed in relation to water quality monitoring and aging sources of fecal contamination. We identified taxon orders that are potential indicators of fresh cattle sources (Oscillospirales and Bacteroidales) and aged sources (Peptostreptococcales-Tissierellales) in water bodies. The paper highlights that bacterial metagenomic profiling can inform our understanding of the ecology of microbial communities in aquatic environments and the potential impacts of agricultural activities on ecosystem health.

Assessing groundwater ecosystem health, status, and services

The concept of ecosystem health is now widely used to communicate the status or condition of a natural environment and is embedded in environmental policies globally. The concept has underpinned ecological assessments for decades but has only recently been applied to groundwater ecosystems. The aim of this chapter was to provide a critical review of current methods for monitoring and assessing the health of groundwater ecosystems, and a discussion of future directions to progress the understanding of ecosystem health, and the provision of ecosystem services in groundwaters.

Effects of native plants on nitrogen cycling microorganisms in soil

Plants modify the nitrogen (N) cycle in soil through plant N uptake, root exudation, and nitrification inhibition resulting from root exudates and changes to the physicochemical properties of soil. Plants with specific traits can be selected to manage N fluxes in the soil following the land application of N-rich wastes thereby reducing losses of N from these systems into the atmosphere (via nitrous oxide) and waterbodies (via nitrate). Previous work has shown that some New Zealand native myrtaceous species can reduce such losses more than other species, but the underlying mechanisms are unknown. It was hypothesized that lower N losses may result from the inhibition of nitrification and denitrification. We aimed to determine the effect of New Zealand native plant species on the abundance of nitrifying and denitrifying microorganisms in the soil using a pot experiment with five native plant species (Carex secta, Coprosma robusta, Kunzea robusta, Leptospermum scoparium, and Metrosideros umbellata) and exotic pasture (Lolium perenne). Half of the pots received fertilisation with N (urea), phosphorus, potassium, and sulphur, while the remainder were unfertilised controls. We quantified the abundance of bacteria, archaea, and the functional genes encoding nitrite reductase (nirK, nirS), nitrous oxide reductase (nosZ), and bacterial and archaeal ammonia monooxygenase (amoA) in the rhizosphere of these plants. Results indicated that plant species had a significant effect on the abundance of nosZ and bacterial amoA. In fertilised soil, the abundance of bacterial amoA was lower under mono-than dicotyledonous species. Similarly, the chemical properties of the soil differed between these groups. Monocotyledonous species took up more N and had lower concentrations of mineral N in the rhizosphere. This indicates that the increased competition for N likely reduced the abundance of amoA and therefore nitrification and nitrate losses. The results support the utilisation of species selection to reduce N losses. In particular, monocotyledonous species may be planted in high-fertility environments to mitigate N contami-nation of ground-and surface water. Future work should determine the mechanisms of plant specific interaction with ammonia-oxidising bacteria, although plant uptake can explain some of the observed differences.

Mobilization of Escherichia coli and fecal source markers from decomposing cowpats.

In rural environments, the sources of fecal contamination in freshwater environments are often diffuse and a mix of fresh and aged fecal sources. It is important for water monitoring purposes, therefore, to understand the impacts of weathering on detection of the fecal source markers available for mobilization from livestock sources. This study targets the impacts of rainfall events on the mobilization of fecal source tracking (FST) markers from simulated cowpats decomposing in situ for five-and-a-half-months. The FST markers analysed were Escherichia coli, microbial source tracking (MST) markers, fecal steroids and a fecal ageing ratio based on the ratio between counts of river microflora and total coliforms. There was a substantial concentration of E. coli (104/100 mL) released from the ageing cowpats suggesting a long-term reservoir of E. coli in the cowpat. Mobilization of fecal markers from rainfall-impacted cowpats, however, was markedly reduced compared with fecal markers in the cowpat. Overall, the Bacteroidales bovine-associated MST markers were less persistent than E. coli in the cowpat and rainfall runoff. The ten fecal steroids, including the major herbivore steroid, 24-ethylcoprostanol, are shown to be stable markers of bovine pollution due to statistically similar degradation rates among all steroids. The mobilizable fraction for each FST marker in the rainfall runoff allowed generation of mobilization decline curves and the derived decline rate constants can be incorporated into source attribution models for agricultural contaminants. Findings from this study of aged bovine pollution sources will enable water managers to improve attribution of elevated E. coli to the appropriate fecal source in rural environments.

National Survey of Per- and Polyfluoroalkyl Substances (PFAS) in Groundwater 2022

National Survey of Pesticides and Emerging Organic Contaminants (EOCs) in Groundwater 2018

The 2014 national survey of pesticides in groundwater in New Zealand