Table of Contents
Primary Productivity in Wetlands: GPP & P/R Insights from Thol Bird Sanctuary
Last Updated: August 31, 2025
Introduction
Have you noticed how a pond that looks “alive” in summer can seem thin and quiet in monsoon? That visible pulse is driven by primary productivity — the rate at which aquatic plants and phytoplankton convert light into organic carbon. Gross Primary Production (GPP) and the Photosynthesis/Respiration (P/R) ratio are the best quantitative windows into that pulse.
This post translates the findings from the Ph.D. thesis by M. H. Bhadrecha (2018) on Thol Bird Sanctuary, showing what GPP and P/R tell us about seasonal dynamics, organic load, bird habitat value and management actions needed. Expect verbatim thesis excerpts (with page numbers), plain-English explanations, and practical recommendations.
What the Thesis Measured
The study measured daily Gross Primary Productivity (GPP) and Photosynthesis–Respiration (P/R) ratios in three locations across seasons (summer, monsoon, winter) during 2015–2018 to assess ecosystem metabolism and organic-matter dynamics. The researcher notes:
“The Gross Primary Production and Photosynthesis Ratio found during the study period along with the important field conditions and observations are put-up at Annexure -IX. The Spatio-Temporal variation in GPP was analyzed and the summary for the same is placed at Table no. 5.9.” (p. 90).
Plain English: GPP = how much carbon the system makes daily; P/R = balance between production and consumption. Together they show whether organic matter is accumulating, being consumed, or the system is near steady state.
Key Verbatim Findings
“It is found that the total daily productivity (Gross Primary Productivity – GPP) of Thol Wetland was maximum (12.45 g C/m³/d) in summer season at Location 1 in the year 2016-2017 and the minimum (0.3 g C/m³/d) in monsoon season at Location 1 in the year 2016-2017 against the overall average value of 5.68 g C/m³/d during the study period (Table no. 5.9, Fig. 5.3).” (pp. 90–91).
Plain English: GPP varies hugely — summer spikes (up to 12.45 g C/m³/d) show intense photosynthetic activity (likely phytoplankton + floating plants), while monsoon dilution or turbidity collapses productivity (as low as 0.3 g C/m³/d). The overall average ~5.7 g C/m³/d places Thol in a moderately productive bracket for a seasonal wetland.
“Moreover, the season wise GPP trend is established as summer > winter > monsoon.” (p. 91).
Plain English: This trend (summer highest) is common in reservoirs and shallow wetlands where stable warm water, sunlight and nutrient build-up in summer favor phytoplankton and floating vegetation growth.
“It is found that the P/R Ratio of Thol Wetland was maximum (3.032) in winter season at Location 3 in the year 2017-2018 (Annexure -IX) and the minimum (0.032) in monsoon season at Location 1 in the year 2016 – 2017 (Annexure -IX) against the overall average value of 0.92 during the study period (Table no. 5.10, Fig. 5.5).” (p. 93).
Plain English: A P/R > 1 (e.g., 3.032) means production exceeds respiration — organic matter may be accumulating. Conversely, P/R ≪ 1 (e.g., 0.032) means respiration dominates and organic matter is being rapidly consumed or diluted. The study’s average P/R ≈ 0.92 suggests the wetland is near a steady state, but with significant seasonal swings.
“Moreover, there exists a relationship between Gross Production (P) and Total Community Respiration (R), where P/R = 1 indicates a steady-state community and if the P/R is greater or less than 1 then organic matter either accumulates or is depleted respectively (Zwart and Trivedi, 1994). During the in situ measurements, the Photosynthesis Respiration Ratio is found to be greater than 1 during winter season for all three years of the study period and in summer season during the year 2016-2017.” (pp. 93–95).
Plain English: The thesis confirms established ecology: P/R = 1 is balance; greater than 1 → accumulation; less than 1 → net loss. At Thol, some winters and one summer showed accumulation, probably tied to organic detritus inputs and plant growth dynamics.
“Field observations during the study period revealed that the Wetland water is enriched by organic detritus… There was also a populous growth of emergent aquatic weed lotus – Nelumbo lucifera at this location 1. The big leaves of Nelumbo shades the water keeping it cool and thus allowing for more dissolved oxygen.” (pp. 93–95).
Plain English: Local plants (e.g., Nelumbo) and detritus strongly affect light, temperature and oxygen — all major drivers of GPP and respiration.
Seasonal & Spatial Patterns
- Summer = productivity peak. Warm, stable waters + nutrient accumulation → high GPP (up to 12.45 g C/m³/d).
- Monsoon = low productivity. Turbidity, dilution and flushing reduce GPP (as low as 0.3 g C/m³/d).
- Winter can flip either way. In some years/waterbodies, P/R > 1 (organic accumulation); elsewhere respiration can be strong depending on detritus and microbial activity.
- Location differences: Location 3 generally showed higher P/R trend than Location 1, indicating spatial heterogeneity linked to depth, vegetation cover and inflow patterns.
Why this matters for birds, people & managers
- Food web: Higher GPP supports phytoplankton → zooplankton → benthic invertebrates → fish and waterbirds. Fluctuations in GPP change food availability for migratory birds (Thol supports many waterfowl).
- Oxygen dynamics: High respiration (low P/R) can create oxygen stress for fauna. Monitoring P/R helps detect early signs of hypoxia risk.
- Irrigation & water use: Productive wetlands can accumulate organic matter and influence water quality downstream; managers must balance irrigation demands with ecological functioning.
Practical monitoring & management recommendations
- Seasonal GPP/P/R monitoring — measure at least summer, winter, monsoon to capture extremes.
- Pair productivity with benthic surveys — GPP alone misses food-web consequences; couple with macroinvertebrate indices.
- Manage nutrient inputs — reduce upstream fertilizer runoff to avoid excessive summer blooms that later fuel high respiration.
- Protect vegetated zones (e.g., Nelumbo stands) that buffer temperature and provide habitat, but monitor for excessive detritus accumulation.
- Use P/R as an early-warning metric for organic load accumulation and potential oxygen stress.
FAQs
Q — What is a “good” GPP for a wetland?
A — Values vary widely; Thol’s average ~5.7 g C/m³/d is moderate. Compare locally and seasonally rather than against a single global threshold.
Q — How often should P/R be measured?
A — At minimum seasonally (monsoon/winter/summer). More frequent sampling reveals short-term pulses.
Q — Can managers increase GPP safely?
A — Encouraging native aquatic plants and controlling turbidity can boost photosynthesis — but avoid nutrient over-enrichment that leads to harmful algal blooms and later oxygen deficits.
Author Bio (original researcher)
Researcher: Dr. M. H. Bhadrecha — Ph.D., Department of Zoology, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara (2018). Research supervised by Prof. P. C. Mankodi. This thesis integrates GPP, P/R, benthic communities and sediment analysis to provide an ecosystem-level view of Thol.
Title: Ecosystem Assessment of Thol Bird Sanctuary with Special Reference to Benthic Macroinvertebrate Community — click the title to open the thesis.
Researcher: Dr. M. H. Bhadrecha
Guide (Supervisor): Prof. P. C. Mankodi
University: The Maharaja Sayajirao University of Baroda, Vadodara — click to visit.
Year of Compilation: 2018
Excerpt Page Numbers Used: pp. 57, 89–95, 90–94, Annexure-IX (see thesis for full data tables and graphs).
Additional trusted reference for wetland productivity concepts: Ramsar Convention — Wetland science & ecosystem services. (good non-competitor link for SEO) — https://www.ramsar.org/
Disclaimer
Disclaimer: Some sentences have been lightly edited for SEO and readability. For the full, original research, please refer to the complete thesis PDF linked in the section above.
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