Ecology and Environment Sciences are both branches of the biology. While having considerable overlapping similarities, there are key differences between the two which means their classifications as separate fields of studies is important.
Ecology is a branch of biology that is concerned with the relationship between living organisms and their environment. Environment sciences are a study of the surroundings of humans.
Environment sciences evaluate the interaction that humans have with their environment. It is studied primarily with a biological focus, expanding on the effects human beings have on their surroundings, but also has aims of securing the environment, and as such, also encompasses the field of ethics, pollution control, environmental sociology as well as politics and law. In environmental sciences, organisms other than humans are classified as part of the environment. Environmental sciences do not just look at studying the environment, but also in finding solutions to environmental problems.
Ecology on the other hand is a discipline that studies the relationship that all living organisms (plants, animals, bacteria) have with their physical, non living (abiotic) environment. This abiotic environment includes light sources, heat radiation, and oxygen availability, nutrients available in the soil, the general atmosphere, and water bodies.
Living organisms are the focus of study in ecology, but the unit of evaluation is the environment. How do living organisms react to changes in their abiotic environment, and what elements, including living organisms affect it are the key questions ecology looks to answer. Ecology also looks to study the relationship different living organisms have on one another- the rise and fall of species as dependent on other species not just the environment. Ecology has no further aims aside from exploring these relationships, and as such is a purely scientific field, unlike environmental sciences which is inter-disciplinary.
Ecology can be seen as a subset of environmental sciences, as it hones down and becomes more specific in addressing the broader themes present in environmental sciences.