Trophic state changes of semi-arid reservoirs as a function of the hydro-climatic variability

Abstract Aim Global patterns of temperature and precipitation have significantly changed over the last century and nearly all predictions point to even greater changes by the end of 2100. Long periods of drought in semi-arid regions generally reduce reservoirs and lakes water level, increasing the nutrients concentrations in the water. Our principal hypothesis is that water volume reduction, driven by prolonged droughts, will increase reservoirs susceptibility to eutrophication and accordingly an increase in trophic state. To test this hypothesis, we used a comparative analysis of ecosystems in a space-for-time substitution approach, in a Brazilian semi-arid region, to predict the consequences of reservoirs water volume reduction on key limnological variables. Methods We sampled 16 reservoirs located in two sub-basins with contrasting rainfall regimes, inserted on Piranhas-Açu watershed. The Seridó River basin (SB) is dry and the Piancó River basin (SB) is humid, with annual mean precipitation of 500 and 700 mm, respectively. Linear regressions analyzes were performed to assess whether the percentage of maximum volume stored (%MVS) is a good predictor for total phosphorus (TP), total nitrogen (TN) and chlorophyll-a (CHLA). In addition, a two factorial analysis of variance (two-way ANOVA) was performed to test for period (dry, very dry and extremely dry), basin (SB and PB) and their interactions effects on TP, TN, CHLA, conductivity, turbidity, and Secchi depth. Results The results showed a reduction in the reservoirs %MVS both for PB and SB regions. At the extremely dry period, all reservoirs were classified as eutrophic, but TP concentrations reached much higher values in SB than in PB. The linear regressions analyses showed that the TP and TN were negatively related to %MVS during all periods sampled. The two-way ANOVA showed that there were significant basin and period effects on TP, TN, Secchi depth and turbidity, whereas for CHLA and conductivity only basin effects were observed. In addition, we found significant interaction effects between period and basin on TP, TN and turbidity. Conclusions We conclude that the contrasting levels of rainfall observed between the two basins affect the water quality and trophic state of the reservoirs and these effects are magnified by water volume reduction. Therefore, our findings might help to predict the consequences of rainfall reductions on freshwater ecosystems of Brazilian drylands.

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Climate vulnerability assessment in semi-arid and arid region of Rajasthan, India: An enquiry into the disadvantaged districts

Journal of Agrometeorology ◽

10.54386/jam.v21i2.233 ◽

2021 ◽

Vol 21 (2) ◽

pp. 197-202

Author(s):

NAVEEN P. SINGH ◽

SURENDRA SINGH ◽

BHAWNA ANAND ◽

S. K. BAL

Keyword(s):

Adaptive Capacity ◽

Crop Production ◽

Climatic Variability ◽

Composite Index ◽

Production Loss ◽

Sensitivity Level ◽

Climate Vulnerability ◽

High Level ◽

Semi Arid ◽

Production Losses

This paper assesses the district level climate vulnerability in the state of Rajasthan using largescale data on climate and socio-economic variables.More than thirty indicators segregated into four components of exposure, sensitivity, adaptive capacity and crop production loss were combined to develop a composite index of vulnerability and homogenous districts were clustered into three categories, viz.low, medium and high.Wide inter-district variations were observed across the calculated indices. The result reveals that highest production losses occurred in Ganganagar district followed by Hanumangarh and Bharatpur. Pali was least exposed to the climatic variability, whereas Bundi had the maximum exposure.Jaisalmer rated the maximum sensitivity level. Further, Pratapgarh followed by Jaisalmer and Banswara had the lowest degree of adaptive capacity. On the whole, districts like Hanumangarh, Jaisalmer, Ganganagar, Bundi, Bharatpur, Jodhpur, Bikaner, Chittorgarh, Alwar, Baran and Pratapgarh exhibit high level of vulnerability to climatic change. While on the other spectrum Sirohi district was least vulnerable due to lower exposure, sensitivity, crop production loss and high adaptive capacity. The analysis, suggests the need for prioritizing vulnerable areas to arrest regional imbalances by encouraging need/location based interventions for moderating the degree of vulnerability, whilst making agro-ecosystem in Rajasthan resilient to climatic aberrations.

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Conservation cropping systems for the semi-arid tropics of North Queensland, Australia

Australian Journal of Experimental Agriculture ◽

10.1071/ea9910515 ◽

1991 ◽

Vol 31 (4) ◽

pp. 515 ◽

Cited By ~ 4

Author(s):

AL Cogle ◽

RJ Bateman ◽

DH Heiner

Keyword(s):

Large Scale ◽

Crop Yields ◽

Cropping Systems ◽

Climatic Variability ◽

Cropping System ◽

Farming Systems ◽

Reduced Tillage ◽

No Tillage ◽

Eastern Australia ◽

Semi Arid

A farming systems project was commenced in the semi-arid tropics of north-eastern Australia to assess the cropping potential and reliability of a newly developing region. Emphasis was placed on evaluation of conservation cropping systems, since it was expected that these would be the most successful and protective uses of the land. This paper discusses the agronomy of peanuts, maize and sorghum grown under different conservative cropping practices (reduced tillage, no tillage, ley) on the soil (red earth) most likely to be developed for large-scale cropping in the region. Crop yields with all practices were limited by establishment difficulties including high soil temperatures, poor weed control and climatic variability. Reduced tillage was more successful than no tillage due to higher yields in dry years; however, in wet years no tillage produced similar yields. The ley cropping system may have some advantages in this environment for integrated production and resource protection.

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