Analysis of spatial changes in physicochemical indicators and their effect on primary production (chlorophyll-a) on the southern coast of the Caspian Sea using a hierarchical regression model

Nahavandian, Somayeh; Arjmandi, Sedigheh; Mahmoudi, Nemat

doi:10.48311/jfst.2026.117627.82459

Analysis of spatial changes in physicochemical indicators and their effect on primary production (chlorophyll-a) on the southern coast of the Caspian Sea using a hierarchical regression model

Document Type : Original Research

Authors

Somayeh Nahavandian ¹

Sedigheh Arjmandi ²

Nemat Mahmoudi ³

¹ Tarbiat Modares University, Faculty of Natural Resources and Marine Sciences, Department of Marine Physics

² Department of Marine Physics, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor

³ Department of Aquaculture, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor

10.48311/jfst.2026.117627.82459

Abstract

This study investigated the spatial variability of key physical parameters and their role in controlling chlorophyll-a distribution on the southeastern continental shelf of the Caspian Sea, focusing on the coastal waters of Babolsar, Nowshahr, and Ramsar. Field measurements were conducted in spring 2012 using a CTD profiler, with data processed according to the TEOS-10 standard. The mixed layer depth was calculated using a density threshold of 0.5 kg.m⁻³, revealing significant spatial variations ranging from 5 m to 16 m across the study area. Analysis of variance revealed significant spatial differences in salinity, dissolved oxygen, and chlorophyll-a concentrations, but not in temperature. A strong inverse pattern was observed, with the highest salinity in Babolsar (13.95 g.kg⁻¹) coinciding with the lowest chlorophyll-a, and the lowest salinity in Nowshahr (13.34 g.kg⁻¹) corresponding to the highest chlorophyll-a. A hierarchical regression model identified salinity (β = -0.651) and temperature (β = -0.525) as significant negative predictors, collectively explaining 46.3% of the variance in chlorophyll-a. These results demonstrate that primary production in this region is predominantly controlled by physical processes regulating nutrient availability.

Keywords

Chlorophyll-a

Mixed Layer Depth

Salinity

Temperature

Southern Caspian Sea

Subjects