I don't think there is a specific protocol. Each component of the pond ecosystem requires different skills to sample, and much depends on what level of study you are intending - energy or nutrients transfer, competition behaviour, or physiological. A complete study would take many months of work, preferably by a small team, so you have to decide on your main focus.
I would start by listing the main components of the pond - e.g. water chemistry, benthic macrophytes, littoral and epiphytic algae, emergent marginal plants, zooplankton and phytoplankton, macroinvertebrates, fish and amphibians, and determine which are most important. Construct a simple flow-diagram to show presumed interactions. Then decide which to sample. In some cases water chemistry may be approximated by pH, dissolved oxygen and conductivity measurements, but you need to sample water for chemistry and temperature at the shore, in the centre and at depth to determine any stratification.
Forms of protocol, that we use in Ukraine, you can find in publication.
Development of European approaches to biological assessment of the state of hydroecosystems and their application to the monitoring of Ukrainian Rivers
I fully agree with Dr. Jullian because you can study any ecosystem with your desired angle and parameters and protocols will differ. Therefore you specify that what exactly you are going to estimate.
you can use protocols from APHA for physical characters and for estimation of biotic component you have to search for various indices depending on what exactly the parametr is.
You may also want to look at the protocols from the US Geological Survey's NAWQA (National Water Quality Assessment) Program. "The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to develop long-term consistent and comparable information on streams, rivers, ground water, and aquatic systems in support of national, regional, State, and local information needs and decisions related to water-quality management and policy."
These protocols cover the gamut from physical through biological components of aquatic systems.
Soendergaard, M., Jeppesen, E., Peder Jensen, J., & Lildal Amsinck, S. (2005). Water Framework Directive: ecological classification of Danish lakes. Journal of Applied Ecology, 42(4), 616-629.
Regards
Simon
Article Water Framework Directive: Ecological classification of Danish lakes