the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Temporal shift of groundwater fauna in South-West Germany
Abstract. Groundwater is an important source of freshwater, drinking water and service water for irrigation, industrial and geothermal uses and the largest terrestrial freshwater biome of the world. In many areas, this habitat is naturally or anthropogenically threatened. This study uses long-term groundwater data from South-West Germany to identify shifts in groundwater fauna due to natural or anthropogenic impacts. Comprehensive analysis of metazoan groundwater fauna and abiotic parameters from 16 monitoring wells over two decades revealed no overall temporal trends for fauna abundance, biodiversity in terms of number of species, as well as no significant large-scale trends in abiotic parameters. While nine wells out of 16 show stable ecological and hydro-chemical conditions at a local level, the remaining wells exhibit shifting or fluctuating faunal parameters. At some locations, these temporal changes are linked to natural causes, such as decreasing dissolved oxygen contents or fluctuating temperatures. A multivariate PHATE (Potential of Heat-diffusion for Affinity-based Trajectory Embedding)-analysis suggests that, beside the hydrogeological setting, varying contents of sediment and detritus impact faunal abundance. By examining aerial images of the surroundings of individual wells, we found that anthropogenic impacts, such as construction sites, can cause significant shifts in groundwater fauna and changes in the ecological status. However, variable faunal composition and abundances were also observed for sites with very stable abiotic conditions in anthropogenically less affected areas. These findings indicate that hydro(geo)logical changes and surface conditions, such as land use, should be assessed in line with hydro-chemical parameters to better understand changes in groundwater fauna. Accordingly, reference sites for natural conditions in ecological assessment and biomonitoring schemes for groundwater protection should be selected carefully.
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RC1: 'Comment on hess-2024-29', Anonymous Referee #1, 17 Apr 2024
1. The MS provides a thorough overview of the study, including the use of long-term groundwater data to identify shifts in groundwater fauna due to natural or anthropogenic impacts. However, providing specific examples or anecdotes from the research could help to make the abstract more engaging and informative.
2. The MS could benefit from a clearer statement of the research objectives and hypotheses, to help readers better understand the purpose of the study.
3. The mention of the PHATE analysis could be expanded upon to provide more detail on this methodology and how it was applied in the study.
4. The abstract mentions the importance of considering hydro(geo)logical changes and surface conditions in assessing changes in groundwater fauna, but it could be helpful to provide more specific recommendations for future research or management strategies based on the study findings.
5. Clarifying the specific types of anthropogenic impacts that were observed, such as pollution sources or land use changes, could help to provide a more nuanced understanding of the study results.
Citation: https://doi.org/10.5194/hess-2024-29-RC1 -
RC2: 'Comment on hess-2024-29', Anonymous Referee #2, 08 May 2024
This is a valuable piece of research and, with some additional statistical analysis and clearer aims, the extensive dataset summarising changes in groundwater ecosystems over a long -period of time will contribute to the knowledge of groundwater ecosystem. I find the manuscript in its current form hard to read and in some points confusing, due to the use of English and the lack of structure. The three major concerns I have as summarised as 1. sampling methodologies & details 2. some statements are oversimplifying these complex ecosystems, 3. some correlations and inferences are being made without sufficient statistical evidence.
It is suggest that
- the manuscript requires a thorough edit for English. There are too many issues to correct by a reviewer. There are numerous grammatical errors and use of words that make little sense in the context of the text.
- Aims and research questions need to be more clearly articulated
- The report structure makes the research hard to understand and the reader would benefit from a clearer structure addressing the studies aims (potentially in subsections). Concepts are scattered throughout the paper, for example temperature and sediment are discussed in line 233- however I cannot find these result anywhere until the discussion (4.4)- and there doesn’t appear to be any statistical analysis of temperature and biota? There are some results presented in the results section, and others in the discussion section. The paper would benefit from a clear discussion section which is entirely separated from the results. This would allow the main aims of the paper to be discussed and compared to previous literature in one section, separated by clear sub-headings. For example, most of discussion section 4.4 is results not discussion, this should be moved to section 3.1 with results explained clearly in the discussion section following.
- The authors should consider additional analysis to detail the relationships between biotic and abiotic factors. Currently, a number of comparisons of fauna to abiotic factors (e.g. sediments, nitrate and dissolved oxygen) are made, but there is no clear analysis of these parameters. The conclusions made regarding ‘clear links’ between for example, DO and groundwater composition are, at this stage, unsubstantiated (eg line 340, 370)
- Whilst it is understood that there are limitations with the use of historic data in terms of sample collection, there are numerous papers that indicate the issues of using nets to sample groundwater ecosystems without purging wells prior to sampling (including Hahn & Matzke 2005; Sorenson et al 2013; Hancock & Boulton 2009; Korbel et al 2017). The number of species and presence/absence of taxa can possibly be reported with some degree of confidence; however the composition of communities is much harder to describe when wells have not been purged (see https://www.iesc.gov.au/sites/default/files/2024-05/bioassessment-groundwater-ecosystems-1.pdf and https://www.iesc.gov.au/sites/default/files/2024-05/bioassessment-groundwater-ecosystems-2.pdf). This is presumably due to specific species habitat & breeding preferences, the artificial well environment as well as the integrity of any well capping. This does not mean that the data cannot be reported as there are some interesting findings, however these issues, at a minimum, need to be discussed in some detail and justifications given for the conclusion made
- The abiotic conditions are also likely to be impacted by the sampling methodology and lack of purging. Water chemistry is usually studies after wells have been purged (generally a minimum of three times or until water is stable). This is a major concern for this study, the lack of any significant changes abiotic parameters over the year may simply reflect the artificial well environment being sampled rather than being representative of the wider aquifer?
Specific comments:
Introduction
The main literature is adequately covered in the introduction. There could be more focus given on the importance of long-term data. You could consider making comparisons to long term data sets used for the management of surface aquatic ecosystems, the benefits of such long term studies and how they translate/ inform management directions. This could be incorporated into paragraph starting line 59.
e.g. line 28-30, English is not correct. Sentence needs re-writing .
Line 49- issues with formatting are apparent.
Methods
More detail on the groundwater sampling process is required (also bailer not bailor).
- Need to state wells are unpurged if this is the case
- How was DO taken, was it using a flow through systems (otherwise please recognise this as a limitation of the design if bailers used)
- Please specify the exact chemical analysis undertaken (line 127) and remove the 'etc'.
- Details on how were samples stored/ preserved is required… if this is in supplementary material please refer to this here.
- What magnification were samples sorted under?
- Line 138- what is LUBW?
Line 195. You mention wells dominated by Tardigrades however I cannot find the results for this measure?
Statistical analysis
- Please provide more detail on the PHATE analysis
- The description of stable and unstable conditions needs to be defined better in the text of the manuscript
- this paper would benefit from a multivariate analysis comparing the fauna to abiotic factors. This would allow investigation into what is causing the changes in biotic communities. e.g.Line 195-200 there is a link between DO and decreased abundance there is a need for some statistical analysis here, maybe on a broader scale looking at DO and fauna abundances and richness within regions and over years. Lines 235-240 indicate that sediment is responsible for some trends, but I cannot find the statistical analysis that indicates this relationship. This section is a little vague and needs further analysis. This paragraph also lacks references to figures.
Faunistic overview (line 165 onwards)
Total abundance can also be influenced by the time between sampling- has this been considered in the analysis.
The increased abundance of Tardigrades within wells, may simply indicate contamination from the surface (as stated e.g. moss or terrestrial carbon contamination within the well)- rather than a change in the broader aquifer ecosystem- such factor should be included in the discussion section.
Section 4.3: This appears to be results rather than discussion. The discussion here is likely to be very relevant to the paper, but would be improved by a total restructure of the paper.
Section 4.4 : This section needs to be re-written removing the claims not backed by statistical results. It is suggested that the majority of this is moved to the results section, and a new section in the discussion is written addressing the aims of the manuscript and the findings of the results. This section should be restructured to engage more with relevant literature describing the results, rather than presenting results.
- Figure 5: Electrical Conductivity
- Figure 6: what is meant by faunistic and hydrochemical stable/ unstable- more explanation is required
- Figures 7-9 are confusing. What does the picture (presumably oligochaete) with a (1) mean in Fig 7, or the cyclopoida in 2017 with a (6) in fig 7. [ same issues in Figure 9 & 10]. A list of stygophilic/ stygobiont species could be presented/ indicated in current Figures 7-10.
Citation: https://doi.org/10.5194/hess-2024-29-RC2
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