Environmental studies are multidisciplinary because in trying to understand a particular environment works man made or natural it means that you must start to visualize the nodes it connects to. Every environment is a network of connected nodes.

 There are no isolate systems, every nodes have inputs and outputs. Imagine u want to study the impact of solar roofs on a city. In order to do this, you must touch these nodes: city and urban planning, electrical grid and building structure (engineering, social studies, ethnography, medical studies,).

This is mostly about physics and chemistry while math’s is inseparable at all stages.  To name a few important parts of mathematics. Probability and statistics (time series) for stochastic analyzes (chaos in hydrology). Numerical integration flow modelling. Machine learning is also being used nowadays in environmental science. Its more about the approach towards any subject which needs to be multidisciplinary

The next set of disciplines will be the earth sciences. These will include but are not limited to geology, hydrology, oceanography, geophysics, astronomy,meteorology and  climatology. More specialization can be given to any area within the field of studies as you can see is often the case due to relatively large breadth that disciple covers. 

There are also many additional tracts not mentioned her,as a complete and inclusive list would need to cover nearly each and every science,  as each and every science is an exploration into the phenomenon of our environment   or of ourselves to begin with.

In this way, the multidisciplinary approach of environmental studies provides the bases for a holistic method to further understand, study and investigate the natural environmental and anthropogenic phenomena, as well as a way to protect our environment and ecological systems from impactful activities through policies and programs, while providing proper management and stewardship of our natural resources.