Treatment Wetland Plant Harvests as a Tool for Soil Phosphorus Reduction in North Central US Agricultural Watersheds

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is interesting. The authors are recommended to clear a few comments before the publication.

It would be interesting to include a graphic representation of the retention efficiency of P as a function of depth. Such a graphic could provide information regarding the degree of soil penetration of P from fertilizers.

Can the method be applied to all forms of P?

Could the results of this study be the basis of a soil rehabilitation program, promoted among farmers, to reduce the P content that could contaminate surface or underground water sources

 

Author Response

The manuscript is interesting. The authors are recommended to clear a few comments before the publication.

It would be interesting to include a graphic representation of the retention efficiency of P as a function of depth. Such a graphic could provide information regarding the degree of soil penetration of P from fertilizers.

– We agree. Unfortunately, not enough data was collected within the wetland or mesocosm experiment to determine any conclusions regarding P retention efficiency as a function of soil depth. This would be a great addition to the research in future studies to assess the fertilizer soil P penetration and associated plant uptake of P.

Can the method be applied to all forms of P?

- Yes, Olsen P was used in this study since it is highly soluble and plant available and likely to show us a representation of P uptake and retention. Longer term studies (over 2 seasons) would be ideal for determining Total P removal potential from the wetland and mesocosm experiments, as Total P typically takes longer timeframes to show changes.

Could the results of this study be the basis of a soil rehabilitation program, promoted among farmers, to reduce the P content that could contaminate surface or underground water sources

- This is an interesting idea for regenerative agriculture. With enough financial support to ensure the proper equipment and monitoring regimes, this could be an option for farmers to implement to reduce P content that potentially could contaminate water sources. We recommend expanding this study to be longer term to determine P removal efficiency over several growing seasons and several rounds of harvesting. Similarly, supporting farmers by providing multiple options for reuse or disposal of the harvested plant material would make this more sustainable in the long term and over larger spatial scales. There are already strong guidance documents on nutrient management (MDA Ag BMP Manual – Lenhart et al. 2017) and University of Minnesota extension docs, which if paired with plant harvest would provide the best wholistic phosphorus management approach.

Reviewer 2 Report

Comments and Suggestions for Authors

Comments on the paper:

Treatment Wetland Plant Harvests as a Tool for Soil Phosphorus Reduction in North Central US Agricultural Watersheds

 Manuscript ID: water-2854137

The goal of this research is to investigate the effectiveness of wetland plant harvesting in reducing soil phosphorus accumulation in edge-of-field treatment wetlands, ultimately preventing these ecosystems from becoming phosphorus sources and ensuring long-term water quality benefits. The innovative aspect of this paper is the evaluation of wetland plant harvesting as a potential solution, with experiments demonstrating reductions in soil phosphorus ranging from 1% to 50% over one year. This method not only addresses the immediate concern of phosphorus runoff, but also provides a flexible adaptation mechanism for land managers facing changing environmental conditions exacerbated by climate change, such as increased heavy rainfall events and flooding. However, several limitations should be acknowledged. These include the potential challenges of generalizing findings beyond the specific geographic region studied, the relatively short temporal scope of the research, potential confounding variables not fully accounted for, uncertainties regarding statistical robustness, practical implementation hurdles, and incomplete exploration of how climate change may affect the effectiveness of wetland management. Addressing these limitations could improve the applicability of the study and provide a more nuanced understanding of vegetation harvesting as a management strategy in agricultural watersheds.

To improve this paper, I would like to comment as follows:

Plant species names should be in italics, please revising throughout the manuscript.

ABSTRACT

Could you provide more details on the specific wetland plant species used in the experiments and include more results in your abstract?

The keywords should be chosen more carefully to better reflect your work; for example: Agricultural watersheds; best management practices; wetland plant harvesting, etc.

INTRODUCTION:

The introduction commendably highlights the key role of wetlands in mitigating nutrient excess and addressing water quality concerns in agricultural watersheds, and the importance of treatment wetlands as an effective management tool. However, while it effectively highlights the challenges posed by nutrient loading and changing climatic conditions, it could benefit from more explicit links between these challenges and the proposed research objectives.

Should you omit the subheading in the introduction and merge all paragraphs?

MATERIAL AND METHODS:

University of Minnesota Mesocosm Experiment

Can you explain the rationale behind the selection of five wetland species for assessment of plant biomass and phosphorus content during the 2018-2019 seasons?

What specific methods were used to simulate agricultural runoff in the mesocosm tanks during the 2018 experiment season, and why was this simulation necessary?

How were the bulrush species monitored and sampled throughout the growing season, and what criteria were used to select the distinct sampling dates?

Describe in more detail how soil samples were collected and analyzed for Olsen P at the beginning and end of each growing season?

Edge-of-Field Treatment Wetland in South-Central Minnesota

Can you provide a map with coordinates to locate the study area?

Describe in detail the methods used to assess phosphorus levels in both wetland vegetation and soil samples collected from treatment wetland cells.

RESULTS

The colors in Figure 1 are confusing; please use different colors for the histograms.

Can you explain the significance of the phosphorus removal rates observed in the mesocosm experiment and their implications for nutrient management strategies in wetland ecosystems?

What factors might have contributed to the differences in phosphorus content between softstem bulrush and river bulrush species in the 2018 experiment season, and how did these differences influence phosphorus removal rates?

How did the seasonal variability in plant biomass and phosphorus content impact the overall phosphorus removal capacity of the wetland vegetation in the mesocosm experiment?

How were the observed reductions in soil phosphorus levels interpreted in the context of nutrient management?

Were there any unexpected findings or challenges encountered during the analysis of soil phosphorus content, and how were these addressed in the interpretation of the results?

What implications do the observed trends in soil phosphorus reduction have for the long-term sustainability and effectiveness of wetland plant harvesting as a nutrient management strategy?

Edge-of-Field Treatment Wetland Case Study

Species biomass and P uptake:

How do the phosphorus removal rates observed in the Granada treatment wetland compare across different monitoring seasons, and what factors might contribute to variations in removal rates?

Can you elaborate on the methods used to estimate phosphorus removal from the wetland area through vegetative harvest, and how were these estimates derived?

What implications do the observed trends in phosphorus removal rates have for the effectiveness of the treatment wetland in mitigating nutrient pollution in the adjacent water bodies?

How does the variability in soil phosphorus content over different sampling seasons reflect changes in nutrient dynamics within the wetland ecosystem, and what factors might contribute to these changes?

Granada wetland soil P:

What insights do the trends in soil Olsen P reductions provide regarding the effectiveness of vegetation harvesting as a nutrient management practice in the Granada treatment wetland?

How do the observed changes in soil phosphorus content align with broader goals of wetland restoration and water quality improvement in the Minnesota River Basin?

Discussion

-Plant harvesting as management practice for reducing soil P

Can you elaborate on the mechanisms by which plant harvesting contributes to reducing soil phosphorus in agricultural wetland soils, and how does this practice fit into broader nutrient management strategies?

What factors might influence the effectiveness of plant harvesting as a management practice for reducing soil phosphorus, and how do these factors vary between the mesocosm experiments and the field-scale wetland site?

Given the variability observed in soil phosphorus reduction rates between mesocosm tanks, what lessons can be learned about the potential effectiveness of plant harvesting as a scalable approach to soil phosphorus remediation in agricultural wetlands?

How do the results of this study compare to existing research on the efficacy of plant harvesting for nutrient management in agricultural wetlands, and are there any new insights or implications derived from your observations?

Given the potential trade-offs between agricultural productivity and wetland ecosystem services, what are the key considerations for land managers when implementing plant harvesting practices in edge-of-field treatment wetlands?

What are the potential long-term effects of annual plant harvesting on the overall health and functioning of the wetland ecosystem, and how might these be mitigated or managed?

Can you discuss any limitations or uncertainties associated with the assessment of phosphorus removal by plant harvesting, and how these might affect the interpretation of the results?

Implications for treatment wetland vegetation harvesting as a management practice in Minnesota and the north central United States

How do the findings of this study inform the selection of wetland plant species for harvesting, and what considerations should be taken into account when determining the optimal timing for vegetation harvests to maximize phosphorus removal efficiency?

Given the predicted increase in precipitation and associated challenges with higher water levels and flooding in the upper Midwest due to climate change, how might these factors impact the effectiveness of wetland vegetation harvesting for nutrient removal in treatment wetlands?

What are the potential limitations or constraints associated with implementing wetland vegetation harvesting for phosphorus remediation in different types of wetland ecosystems, and how might these vary between shallow wetlands, deep marshes, and forested swamps?

Can you discuss the implications of wetland vegetation harvesting practices on the overall ecological health and functioning of treatment wetlands, particularly in terms of biodiversity, habitat quality, and ecosystem resilience?

Are there any regulatory or policy considerations that need to be taken into account when implementing wetland vegetation harvesting practices, and what frameworks or guidelines exist to support sustainable and responsible management of treatment wetlands?

How do the findings of this study contribute to broader discussions around sustainable agriculture and water quality management in the context of intensively managed agricultural landscapes?

Can you discuss any potential trade-offs or synergies between wetland vegetation harvesting and other management strategies for nutrient reduction in agricultural watersheds, such as cover cropping, buffer strips, or controlled drainage systems?

Role of plant harvest in climate change adaptation

Can you elaborate on the mechanisms by which wetland vegetation interacts with saturated soils under different hydrologic conditions, and how this may affect phosphorus uptake and removal efficiency in the context of climate change?

What are the potential effects of climate change on the nutrient removal capacity of wetlands, and how might these effects vary among different wetland ecosystem types and geographic regions?

What are the key considerations for land managers and policy makers in designing and implementing wetland restoration programs to enhance nutrient removal benefits, given the potential trade-offs between agricultural productivity and ecosystem service provision?

Can you provide examples of successful wetland restoration projects that have effectively reduced downstream nutrient loading in agricultural watersheds, and how have these projects been scaled up or replicated to achieve broader environmental benefits?

Can you discuss potential synergies or conflicts between wetland conservation efforts and other climate change adaptation strategies in agricultural landscapes, and how these can be managed to optimize overall ecosystem resilience and sustainability?

Conclusions

The conclusion needs to be revised to include all the key findings of this study.

What are the key factors that land managers should consider when implementing vegetation harvesting practices in edge-of-field treatment wetlands, and how can these practices be optimized to maximize nutrient removal efficiency while minimizing potential negative impacts on wetland ecosystems?

What are the implications of this study for policy development and implementation related to wetland conservation and nutrient management in agricultural landscapes, particularly in the context of water quality regulation and climate change adaptation?

 

 

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors addressed all the inquiries, resulting in an enhanced quality of the paper