The best indicator of ecological changes, as far as an aquatic ecosystem is considered is the primary producers  - Phytoplanktons. The changes with them directly and indirectly affect that  ecosystem as a whole. 

Please find the attached. Some way, it may help you. 

All the Very Best

Anila Ajayan

Climate change is larger event basically deals with temperature across the globe rest are change in landuse patterns The internal flora of the which has long life span in the lake system can be a good  indicator rest all do change with season.

the marsh vegetation  of the wetland is one of the good indicator of impact.

I'd be looking for changing species abundances,  new species occurrences/ establishment, changing phenology or changing dates of arrival or departure of migratory species,  increased incidence of extreme events like algal blooms.

I would say that it depends on the available data.... and also the time range that you want to document....

Also consider having assessment evolutionary qualitative indicators from communities and peoples living in and around the ecosystem since centuries. they could help with some practical and living changing markers than you could then verify with different GIS data or methods.  

Agree with all the comments given by experts and I would like to suggest the following references.

1.Jadwiga Sienkiewicz , Apolonia Ostrowska, Katrin Vohland, Lars Stratmann, Mateusz Grygoruk, Indicators for Monitoring Climate Change-Induced Effects on Habitats – A Wetlands Perspective

2. John P Smol and Eugene F Stoermer, The Diatoms: Applications for the Environmental and Earth Sciences

The best indicator of ecological changes, as far as an aquatic ecosystem is considered is the primary producers  - Phytoplanktons. The changes with them directly and indirectly affect that  ecosystem as a whole. 

Please find the attached. Some way, it may help you. 

All the Very Best

Anila Ajayan

I thank thezooplankton can ba also a very good indicator...in relation with the temperature...

I would look in to pollen/spore abundances to assess climate induced vegetation changes. This requires that you have sediment accumulation is lakes or small ponds or bogs.

Good luck,

Yuki

Climate change is a big event takes decades to occur mostly the temperature is taken as a factor

but for indicator of wetland change due to ecological changes you can look on to the floral components of the lake, those flora which stands for years if the number is increasing or decreasing can be a stable indicator rest all are changing as seasonal variation occurs.

those flora whose life span is large , marsh vegetation of the pond side etc.

Number of bird species , fishes and plankton etc are indicator of health of wetlands.

An important question - are you looking at ways to monitor changes in a living wetland system, or to detect climate change in the past through sediment cores, etc.?  

If you are looking at past environments, try to obtain as much information as possible from your core or cores.  As mentioned above, the vegetation is key because usually the plants form the framework for the ecosystem and as climate changes the vegetation shifts, and the entire ecosystem shifts.  So analyzing the macroplants and pollen in a core is very important.  Also, any other biotic remains - diatoms, mollusks if fresh; diatoms, mollusks, forams, ostracodes, etc. if coastal/salt marsh wetlands.  Isotopic analyses of the organisms can indicate temperature.  Geochemical analyses of the sediments can provide clues to the depositional environment.  Also, grain size analyses and studying the layering within the cores can be indicative of storms, changes in sea level/water level, etc.

I would agree with everyone's response, especially from Liz Dovey and G. Lynn Wingard. Current climate change is being evaluated by phenology monitoring of many organisms. The mismatch of flowering and seed production with butterfly and bird migrations is a case in point.

Phytoplankton spore flowering is highly dependent on temperature regime & is one of the easy & sure shot item to discern climate change.

for brackish water wetland its salinity and phytoplankton

Hi,

I agree with most statements already made, but I would like to add:

-  timing and extent of flood events is very likely to change and these factors are of paramount importance for the ecosystem.

Unfortunately, changes in hydrology are diffucult to prove due to the large "natural" variablity in hydrological conditions. Still, it cannot be ignored (I think).

kind regards

Irene

The best ecological indicator of climate change in a wetland ecosystem is the sudden change in number and type of birds coming to that wetland. This statement is more important in case of migratory birds. Changes in wetland habitats should also be given importance while observing any changes in number and type of birds. 

In semi-terrestrial systems - this could be plants , especially these groups that benefit from release of anoxia constrain - due to more often drought: grasses, shrubs and trees , some ruderal forbs . This is though difficult to set apart form eg an effect of other   degradation pressure (drainage, agriculture). This is actually a major problems for such studies in general - independent of organism you pick as your indicator.

Also an increase in invasive plant species coming form warmer climates can be an indication  (these that woudl normally froze in winter - but due to mild winters  they can spread and reproduce) .

(well - i am biased as i work mainly with plants). 

The term "wetland" includes a wide range of landscapes and process dynamics. Hence, there is not such a thing as the "best indicator" amenable of universal use, Each ecosystem and its component react to any given climate change driver in a different fashion, modulated, in turn, by spatio-temporal and scale factors. In other words, the deviation of 1 degree centigrade in a wetland in Alaska will not have the same impact on ecosystem components and functions of a wetland in South Florida. Finding the "best indicator" for a given site requires a detailed assessment of links between the potential indicator and the specific driver. Instead of giving you a "yellow-cap" indicator, I would recommend you to review published literature in journals like Ecological Indicators (Elsevier), just to mention one

Here is another indicator of climate change: https://www.researchgate.net/publication/292155626_Using_ecoacoustic_methods_to_survey_the_impacts_of_climate_change_on_biodiversity. The model is useful for both marine and terrestrial habitats.

Article Using ecoacoustic methods to survey the impacts of climate c...

The hydroperiod, the pattern of flooding within a wetland, is the biggest driver of the type of wetland habitat that is maintained and the species that it supports. Changes in the hydroperiod - from climate change or other causes - will dramatically alter wetland ecosystems. The species or ecological indicator that can be used to determine if the hydroperiod is changing depends on the wetland type (coastal wetland, bogs, riparian wetlands, etc..) you are looking at - and it will vary. But ultimately, its the hydrology of a wetland that needs to be tracked first to measure if a wetland is changing due to climate change. Temperature and other factors are also important, but secondary. 

Climate change affects the various components of the ecosystem in different ways. However the best ecological indicator of climate change is the temperature regime of the studied wetland. This is because temperature affects the distribution and abundance of both phytoplankton and zooplankton which forms the basis of food chains in wetland ecosystems. In fact temperature directly affects dissolved oxygen.

From all the answers given so far, the following physical variables are important for long term monitoring of climate change impacts on wetland biota:

1. temperature, air and water, water at various depths

2. hydroperiod, including water levels and frequency of drawdowns, drying

3. pH

4. oxygen levels

5. nutrient levels (N, P, Ca, etc.)

Jackson Achankunju suggested above some references, but didn't include where they were from.  The source of the first one of them is: 

Chapter 6 in Sven Rannow & Marco Neubert (Editors) 2014 Managing Protected Areas in Central and Eastern Europe Under Climate Change, Springer

I found this book can be freely downloaded from:

http://www.central2013.eu/fileadmin/user_upload/Downloads/outputlib/HABIT-CHANGE_5_3_2_Management_Handbook.pdf